fix: performance of erfinv #7568

[JeWaVe]

Before :
an array of 1000 double is allocated and computed for each erfinv call

Now :
Lazy allocation for coefficient in a readonly struct with static constructor
Allocation and computation is done only once, first time we invoke erfinv

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.02%. Comparing base (adf0cec) to head (bfefa76).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/Microsoft.ML.CpuMath/ProbabilityFunctions.cs	0.00%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7569      +/-   ##
==========================================
- Coverage   69.02%   69.02%   -0.01%     
==========================================
  Files        1482     1482              
  Lines      274096   274099       +3     
  Branches    28266    28266              
==========================================
- Hits       189191   189187       -4     
- Misses      77518    77526       +8     
+ Partials     7387     7386       -1     

Flag	Coverage Δ
Debug	69.02% <0.00%> (-0.01%)	⬇️
production	63.30% <0.00%> (-0.01%)	⬇️
test	89.47% <ø> (ø)

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Files with missing lines	Coverage Δ
src/Microsoft.ML.CpuMath/ProbabilityFunctions.cs	50.00% <0.00%> (-1.86%)	⬇️

... and 3 files with indirect coverage changes

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[JeWaVe]

There was no tests before. Should I add some ?