Replace Tangents with NTuple

[gdalle]

DI source

• Replace Tangents with NTuple in pushforward, pullback and hvp
• Adjust docstrings

DI extensions

• Replace Tangents with NTuple
• Enzyme and Mooncake: improve fallback structure
• Enzyme: use values because the returns are sometimes NamedTuples

DIT source

• Replace Tangents with NTuple in scenarios

DI tests

• Speed up Enzyme tests
• Reactivate second derivative type stability tests in zero backends

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 99.25926% with 2 lines in your changes missing coverage. Please review.

Project coverage is 98.60%. Comparing base (1307890) to head (5ca95ae).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...t/DifferentiationInterfaceReverseDiffExt/onearg.jl	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #501      +/-   ##
==========================================
+ Coverage   98.43%   98.60%   +0.17%     
==========================================
  Files         106      105       -1     
  Lines        4471     4459      -12     
==========================================
- Hits         4401     4397       -4     
+ Misses         70       62       -8     

Flag	Coverage Δ
DI	98.74% <99.11%> (+0.25%)	⬆️
DIT	98.31% <100.00%> (+<0.01%)	⬆️

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