Fix precision of changebasis

[hyrodium]

This PR fixes #177 (comment).

Before this PR

julia> using BasicBSpline

julia> p = 3
3

julia> P = BSplineSpace{p}(KnotVector([4,4,4,4,5,6,7,7,7,7]))
BSplineSpace{3, Int64, KnotVector{Int64}}(KnotVector([4, 4, 4, 4, 5, 6, 7, 7, 7, 7]))

julia> P′ = BSplineSpace{p}(KnotVector([4,4,4,4,4.5,5,6,7,7,7,7]))
BSplineSpace{3, Float64, KnotVector{Float64}}(KnotVector([4.0, 4.0, 4.0, 4.0, 4.5, 5.0, 6.0, 7.0, 7.0, 7.0, 7.0]))

julia> changebasis(P,P′)
6×7 Matrix{Float64}:
 1.0   0.5          0.0          0.0       0.0           0.0          0.0
 0.0   0.5          0.75         0.0       0.0           0.0          0.0
 0.0  -5.55112e-17  0.25         0.833333  5.55112e-17   5.55112e-17  0.0
 0.0   4.16334e-17  4.16334e-17  0.166667  1.0          -5.55112e-17  0.0
 0.0   0.0          0.0          0.0       0.0           1.0          0.0
 0.0   0.0          0.0          0.0       0.0           0.0          1.0

After this PR

julia> using BasicBSpline

julia> p = 3
3

julia> P = BSplineSpace{p}(KnotVector([4,4,4,4,5,6,7,7,7,7]))
BSplineSpace{3, Int64, KnotVector{Int64}}(KnotVector([4, 4, 4, 4, 5, 6, 7, 7, 7, 7]))

julia> P′ = BSplineSpace{p}(KnotVector([4,4,4,4,4.5,5,6,7,7,7,7]))
BSplineSpace{3, Float64, KnotVector{Float64}}(KnotVector([4.0, 4.0, 4.0, 4.0, 4.5, 5.0, 6.0, 7.0, 7.0, 7.0, 7.0]))

julia> changebasis(P,P′)
6×7 Matrix{Float64}:
 1.0   0.5  0.0   0.0       0.0   0.0  0.0
 0.0   0.5  0.75  0.0       0.0   0.0  0.0
 0.0  -0.0  0.25  0.833333  0.0   0.0  0.0
 0.0   0.0  0.0   0.166667  1.0  -0.0  0.0
 0.0   0.0  0.0   0.0       0.0   1.0  0.0
 0.0   0.0  0.0   0.0       0.0   0.0  1.0

[hyrodium]

The performance is also getting better.
Before this PR

julia> @benchmark changebasis(P,P′)
BenchmarkTools.Trial: 10000 samples with 1 evaluation.
 Range (min … max):  10.760 μs …  2.393 ms  ┊ GC (min … max):  0.00% … 98.54%
 Time  (median):     12.283 μs              ┊ GC (median):     0.00%
 Time  (mean ± σ):   15.404 μs ± 59.374 μs  ┊ GC (mean ± σ):  10.11% ±  2.61%

  ▁▅▇██▇▆▅▄▄▄▃▃▃▃▂▂▁▁   ▁▁▁▂▂▂▂▂▂▂▂▂▂▂▁▂▂▁▁                   ▂
  ████████████████████▇█████████████████████▇█▇▆▇▆▇▇▆▇▆▆▆▅▆▅▆ █
  10.8 μs      Histogram: log(frequency) by time      27.4 μs <

 Memory estimate: 32.36 KiB, allocs estimate: 188.

After this PR

julia> @benchmark changebasis(P,P′)
BenchmarkTools.Trial: 10000 samples with 1 evaluation.
 Range (min … max):   9.328 μs …  2.434 ms  ┊ GC (min … max): 0.00% … 98.59%
 Time  (median):     10.620 μs              ┊ GC (median):    0.00%
 Time  (mean ± σ):   13.163 μs ± 52.199 μs  ┊ GC (mean ± σ):  9.60% ±  2.42%

  ▂▆▇██▇▇▅▄▃▃▂▂▁▂▁▁ ▁▂▂▁▁▂▁▂▁▂▁▂▂▁▁▁▁▁▁▁ ▁                    ▂
  ██████████████████████████████████████████▇▇█▇▇▇▇▇▇▆▅▆▅▆▆▆▆ █
  9.33 μs      Histogram: log(frequency) by time      24.2 μs <

 Memory estimate: 27.30 KiB, allocs estimate: 158.

[codecov]

Codecov Report

Merging #306 (fed5862) into main (e99cb47) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #306   +/-   ##
=======================================
  Coverage   98.46%   98.46%           
=======================================
  Files          13       13           
  Lines        1241     1241           
=======================================
  Hits         1222     1222           
  Misses         19       19           

Impacted Files	Coverage Δ
src/_ChangeBasis.jl	97.94% <100.00%> (ø)

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