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

We are excited to review your PR.

So we can do the best job, please check:

• [x ] There's a descriptive title that will make sense to other developers some time from now.
• There's associated issues. All PR's should have issue(s) associated - unless a trivial self-evident change such as fixing a typo. You can use the format Fixes #nnnn in your description to cause GitHub to automatically close the issue(s) when your PR is merged.
• Your change description explains what the change does, why you chose your approach, and anything else that reviewers should know.
• You have included any necessary tests in the same PR. (didn't see any tests)

[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)

Flags with carried forward coverage won't be shown. Click here to find out more.

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.