Stanc.Std: Move Frontend over

[WardBrian]

Submission Checklist

• Run unit tests
• Documentation
  • If a user-facing facing change was made, the documentation PR is here:
  • OR, no user-facing changes were made

Release notes

Replace this text with a short note on what will change if this pull request is merged. This will be included in the release notes.

Copyright and Licensing

By submitting this pull request, the copyright holder is agreeing to
license the submitted work under the BSD 3-clause license (https://opensource.org/licenses/BSD-3-Clause)

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[codecov]

Codecov Report

❌ Patch coverage is 88.59316% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.21%. Comparing base (fd7702d) to head (21b6ee0).

Files with missing lines	Patch %	Lines
src/std/std.ml	84.21%	9 Missing ⚠️
src/frontend/Typechecker.ml	91.25%	7 Missing ⚠️
src/frontend/Ast_to_Mir.ml	85.18%	4 Missing ⚠️
src/frontend/Deprecation_analysis.ml	75.00%	2 Missing ⚠️
src/frontend/Info.ml	80.00%	2 Missing ⚠️
src/frontend/Ast.ml	90.00%	1 Missing ⚠️
src/frontend/Errors.ml	90.00%	1 Missing ⚠️
src/frontend/Pretty_printing.ml	87.50%	1 Missing ⚠️
src/frontend/Promotion.ml	80.00%	1 Missing ⚠️
src/frontend/Semantic_error.ml	80.00%	1 Missing ⚠️
... and 1 more

Additional details and impacted files

@@              Coverage Diff               @@
##           std/driver    #1659      +/-   ##
==============================================
+ Coverage       92.16%   92.21%   +0.05%     
==============================================
  Files              69       69              
  Lines           10020    10099      +79     
==============================================
+ Hits             9235     9313      +78     
- Misses            785      786       +1     

Files with missing lines	Coverage Δ
src/frontend/Canonicalize.ml	96.36% <100.00%> (ø)
src/frontend/Environment.ml	89.18% <100.00%> (+0.30%)	⬆️
src/frontend/Input_warnings.ml	100.00% <ø> (ø)
src/frontend/Pretty_print_prog.ml	88.23% <100.00%> (ø)
src/frontend/Syntax_error.ml	96.70% <100.00%> (+0.03%)	⬆️
src/frontend/Warnings.ml	100.00% <100.00%> (ø)
src/stan_math_signatures/Stan_math_signatures.ml	86.66% <100.00%> (ø)
src/frontend/Ast.ml	88.41% <90.00%> (ø)
src/frontend/Errors.ml	96.00% <90.00%> (-4.00%)	⬇️
src/frontend/Pretty_printing.ml	94.96% <87.50%> (-0.29%)	⬇️
... and 8 more

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