feat: add non-mutating set_scalar_constants

[MilesCranmerBot]

This adds a non-mutating set_scalar_constants helper that returns a new tree with updated scalar constants.

Motivation (empirical): trying to run ForwardDiff.gradient through set_scalar_constants! on a Node{Float64} fails because constant node fields are concretely typed (e.g. cannot assign Dual into Float64). The new helper promotes the tree number type to accommodate eltype(constants) (so Duals work), sets the constants, and returns the new tree.

Changes:

• Add set_scalar_constants(tree, constants) (non-mutating; promotes number type if needed).
• Add set_scalar_constants(ex::Expression, constants) wrapper.
• Add a regression test demonstrating ForwardDiff gradients w.r.t. constants.

Tests:

• Pkg.test()

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 59.53%. Comparing base (68d60d4) to head (141ecab).

Files with missing lines	Patch %	Lines
src/NodeUtils.jl	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #165      +/-   ##
==========================================
+ Coverage   59.33%   59.53%   +0.20%     
==========================================
  Files          30       30              
  Lines        2673     2684      +11     
==========================================
+ Hits         1586     1598      +12     
+ Misses       1087     1086       -1     

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[github-actions]

Benchmark Results (Julia v1)

Time benchmarks

	master	141ecab...	master / 141ecab...
eval/ComplexF32/evaluation	6.9 ± 0.47 ms	6.88 ± 0.46 ms	1 ± 0.096
eval/ComplexF64/evaluation	10.3 ± 0.75 ms	10.2 ± 0.84 ms	1 ± 0.11
eval/Float32/derivative	11.1 ± 1.1 ms	10.8 ± 1 ms	1.03 ± 0.14
eval/Float32/derivative_turbo	11 ± 1 ms	10.8 ± 0.95 ms	1.03 ± 0.13
eval/Float32/evaluation	2.44 ± 0.24 ms	2.46 ± 0.23 ms	0.992 ± 0.14
eval/Float32/evaluation_bumper	0.598 ± 0.017 ms	0.601 ± 0.016 ms	0.996 ± 0.038
eval/Float32/evaluation_turbo	0.52 ± 0.034 ms	0.526 ± 0.032 ms	0.987 ± 0.088
eval/Float32/evaluation_turbo_bumper	0.598 ± 0.017 ms	0.602 ± 0.017 ms	0.993 ± 0.039
eval/Float64/derivative	14.1 ± 1.8 ms	14.4 ± 1.8 ms	0.979 ± 0.17
eval/Float64/derivative_turbo	14 ± 1.4 ms	14.2 ± 1.4 ms	0.985 ± 0.14
eval/Float64/evaluation	2.87 ± 0.28 ms	2.88 ± 0.27 ms	0.997 ± 0.14
eval/Float64/evaluation_bumper	1.26 ± 0.041 ms	1.26 ± 0.045 ms	0.993 ± 0.048
eval/Float64/evaluation_turbo	1.02 ± 0.064 ms	1.02 ± 0.063 ms	1 ± 0.088
eval/Float64/evaluation_turbo_bumper	1.25 ± 0.044 ms	1.27 ± 0.043 ms	0.986 ± 0.048
utils/combine_operators/break_sharing	0.0424 ± 0.0013 ms	0.0416 ± 0.001 ms	1.02 ± 0.04
utils/convert/break_sharing	28 ± 3.6 μs	27.7 ± 3.6 μs	1.01 ± 0.19
utils/convert/preserve_sharing	0.1 ± 0.01 ms	0.0993 ± 0.0098 ms	1.01 ± 0.14
utils/copy/break_sharing	28.3 ± 4.9 μs	28 ± 4 μs	1.01 ± 0.23
utils/copy/preserve_sharing	0.101 ± 0.0096 ms	0.0988 ± 0.0089 ms	1.02 ± 0.13
utils/count_constant_nodes/break_sharing	13.5 ± 1.2 μs	12.9 ± 0.9 μs	1.05 ± 0.12
utils/count_constant_nodes/preserve_sharing	0.0871 ± 0.0091 ms	0.0858 ± 0.007 ms	1.01 ± 0.13
utils/count_depth/break_sharing	13.9 ± 1.5 μs	14.6 ± 0.98 μs	0.954 ± 0.12
utils/count_nodes/break_sharing	12.7 ± 1 μs	13.1 ± 1.2 μs	0.972 ± 0.12
utils/count_nodes/preserve_sharing	0.0871 ± 0.0082 ms	0.0871 ± 0.0078 ms	1 ± 0.13
utils/get_set_constants!/break_sharing	0.0334 ± 0.0039 ms	0.0331 ± 0.0038 ms	1.01 ± 0.17
utils/get_set_constants!/preserve_sharing	0.174 ± 0.011 ms	0.175 ± 0.011 ms	0.993 ± 0.089
utils/get_set_constants_parametric	0.0449 ± 0.0046 ms	0.0464 ± 0.0063 ms	0.968 ± 0.17
utils/has_constants/break_sharing	7.96 ± 1.6 μs	8.09 ± 1.4 μs	0.984 ± 0.26
utils/has_operators/break_sharing	2.62 ± 0.27 μs	2.65 ± 0.26 μs	0.992 ± 0.14
utils/hash/break_sharing	24 ± 2.3 μs	23.4 ± 1.4 μs	1.03 ± 0.12
utils/hash/preserve_sharing	0.103 ± 0.011 ms	0.102 ± 0.0084 ms	1.01 ± 0.14
utils/index_constant_nodes/break_sharing	29 ± 2.5 μs	29.6 ± 3.3 μs	0.979 ± 0.14
utils/index_constant_nodes/preserve_sharing	0.103 ± 0.01 ms	0.102 ± 0.0083 ms	1.01 ± 0.13
utils/is_constant/break_sharing	8.47 ± 1.5 μs	8.39 ± 1.3 μs	1.01 ± 0.23
utils/simplify_tree/break_sharing	31.2 ± 1.3 μs	31.1 ± 1.4 μs	1 ± 0.063
utils/simplify_tree/preserve_sharing	0.117 ± 0.0094 ms	0.111 ± 0.0071 ms	1.05 ± 0.11
utils/string_tree/break_sharing	0.45 ± 0.022 ms	0.428 ± 0.018 ms	1.05 ± 0.069
utils/string_tree/preserve_sharing	0.55 ± 0.03 ms	0.527 ± 0.023 ms	1.04 ± 0.072
time_to_load	0.167 ± 0.0024 s	0.167 ± 0.0039 s	1 ± 0.027

Memory benchmarks

	master	141ecab...	master / 141ecab...
eval/ComplexF32/evaluation	0.987 k allocs: 2.53 MB	0.987 k allocs: 2.53 MB	1
eval/ComplexF64/evaluation	0.99 k allocs: 5.04 MB	0.99 k allocs: 5.04 MB	1
eval/Float32/derivative	4.62 k allocs: 17.4 MB	4.62 k allocs: 17.4 MB	1
eval/Float32/derivative_turbo	4.7 k allocs: 17.7 MB	4.59 k allocs: 17.3 MB	1.02
eval/Float32/evaluation	0.984 k allocs: 1.28 MB	0.978 k allocs: 1.27 MB	1.01
eval/Float32/evaluation_bumper	0.303 k allocs: 0.393 MB	0.303 k allocs: 0.393 MB	1
eval/Float32/evaluation_turbo	0.96 k allocs: 1.25 MB	0.948 k allocs: 1.23 MB	1.01
eval/Float32/evaluation_turbo_bumper	0.303 k allocs: 0.393 MB	0.303 k allocs: 0.393 MB	1
eval/Float64/derivative	4.81 k allocs: 0.0352 GB	4.77 k allocs: 0.0349 GB	1.01
eval/Float64/derivative_turbo	4.79 k allocs: 0.035 GB	4.76 k allocs: 0.0348 GB	1.01
eval/Float64/evaluation	0.996 k allocs: 2.55 MB	0.99 k allocs: 2.53 MB	1.01
eval/Float64/evaluation_bumper	0.303 k allocs: 0.771 MB	0.303 k allocs: 0.771 MB	1
eval/Float64/evaluation_turbo	0.993 k allocs: 2.54 MB	0.972 k allocs: 2.49 MB	1.02
eval/Float64/evaluation_turbo_bumper	0.303 k allocs: 0.771 MB	0.303 k allocs: 0.771 MB	1
utils/combine_operators/break_sharing	4 allocs: 0.953 kB	4 allocs: 0.953 kB	1
utils/convert/break_sharing	2 k allocs: 0.123 MB	2 k allocs: 0.123 MB	1
utils/convert/preserve_sharing	2.4 k allocs: 0.192 MB	2.4 k allocs: 0.192 MB	1
utils/copy/break_sharing	2 k allocs: 0.123 MB	2 k allocs: 0.123 MB	1
utils/copy/preserve_sharing	2.4 k allocs: 0.192 MB	2.4 k allocs: 0.192 MB	1
utils/count_constant_nodes/break_sharing	4 allocs: 0.953 kB	4 allocs: 0.953 kB	1
utils/count_constant_nodes/preserve_sharing	0.404 k allocs: 0.0696 MB	0.404 k allocs: 0.0696 MB	1
utils/count_depth/break_sharing	4 allocs: 0.953 kB	4 allocs: 0.953 kB	1
utils/count_nodes/break_sharing	4 allocs: 0.953 kB	4 allocs: 0.953 kB	1
utils/count_nodes/preserve_sharing	0.404 k allocs: 0.0696 MB	0.404 k allocs: 0.0696 MB	1
utils/get_set_constants!/break_sharing	0.898 k allocs: 25.2 kB	0.898 k allocs: 25.2 kB	1
utils/get_set_constants!/preserve_sharing	1.7 k allocs: 0.138 MB	1.7 k allocs: 0.138 MB	1
utils/get_set_constants_parametric	1.42 k allocs: 0.0663 MB	1.42 k allocs: 0.0663 MB	1
utils/has_constants/break_sharing	4 allocs: 0.203 kB	4 allocs: 0.203 kB	1
utils/has_operators/break_sharing	4 allocs: 0.203 kB	4 allocs: 0.203 kB	1
utils/hash/break_sharing	0.104 k allocs: 2.52 kB	0.104 k allocs: 2.52 kB	1
utils/hash/preserve_sharing	0.504 k allocs: 0.0711 MB	0.504 k allocs: 0.0711 MB	1
utils/index_constant_nodes/break_sharing	2.1 k allocs: 0.094 MB	2.1 k allocs: 0.094 MB	1
utils/index_constant_nodes/preserve_sharing	2.5 k allocs: 0.163 MB	2.5 k allocs: 0.163 MB	1
utils/is_constant/break_sharing	4 allocs: 0.203 kB	4 allocs: 0.203 kB	1
utils/simplify_tree/break_sharing	0.104 k allocs: 2.52 kB	0.104 k allocs: 2.52 kB	1
utils/simplify_tree/preserve_sharing	0.504 k allocs: 0.0711 MB	0.504 k allocs: 0.0711 MB	1
utils/string_tree/break_sharing	11.9 k allocs: 0.999 MB	11.9 k allocs: 0.999 MB	1
utils/string_tree/preserve_sharing	12.3 k allocs: 1.07 MB	12.3 k allocs: 1.07 MB	1
time_to_load	0.145 k allocs: 11 kB	0.145 k allocs: 11 kB	1