Replace Base with Stdlib and custom shims

[WardBrian]

This PR is unfortunately quite large, but many of the changes are simple renames. Review should focus on the src/std/ folder and the few places where any non-trivial edits were made.

---

This is the ultimate conclusion of the patch sequence #1643 #1644 #1650 #1652.

After updating to 5.5, Base was providing us (up to renaming) essentially just:

• Polymorphic sets
• Hash sets
• A few small quality of life functions

These are all easy to provide ourselves, which means we can remove the dependency entirely.

The binaries produced with dune build --profile release from this branch are 12mb, down from 15mb on master. Shockingly, they're also the same speed if not faster (especially when running optimizations):

Summary
  ./stanc-nobase ./test/integration/good/code-gen/mother.stan ran
    1.03 ± 0.07 times faster than ./stanc-master ./test/integration/good/code-gen/mother.stan

Summary
  ./stanc-nobase --O1 ./test/integration/good/compiler-optimizations/copy_fail.stan ran
    1.56 ± 0.10 times faster than ./stanc-master --O1 ./test/integration/good/compiler-optimizations/copy_fail.stan

Summary
  ./stanc-nobase --Oexperimental ./test/integration/good/compiler-optimizations/copy_fail.stan ran
    2.03 ± 0.16 times faster than ./stanc-master --Oexperimental ./test/integration/good/compiler-optimizations/copy_fail.stan

Javascript builds are down to 16mb from 19mb, with minified sizes roughly the same.

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

Decreased our reliance on third-party packages

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)

[codecov]

Codecov Report

❌ Patch coverage is 92.00426% with 75 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.28%. Comparing base (ac69570) to head (29e783f).

Files with missing lines	Patch %	Lines
src/analysis_and_optimization/Factor_graph.ml	78.26%	10 Missing ⚠️
src/std/std.ml	90.56%	10 Missing ⚠️
src/frontend/Typechecker.ml	91.02%	7 Missing ⚠️
src/std/Hash_set.ml	44.44%	5 Missing ⚠️
...analysis_and_optimization/Debug_data_generation.ml	86.20%	4 Missing ⚠️
src/analysis_and_optimization/Memory_patterns.ml	90.90%	4 Missing ⚠️
src/analysis_and_optimization/Mir_utils.ml	81.81%	4 Missing ⚠️
src/frontend/Ast_to_Mir.ml	85.18%	4 Missing ⚠️
...rc/analysis_and_optimization/Monotone_framework.ml	97.58%	3 Missing ⚠️
src/analysis_and_optimization/Optimize.ml	94.82%	3 Missing ⚠️
... and 15 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1655      +/-   ##
==========================================
- Coverage   92.33%   92.28%   -0.06%     
==========================================
  Files          67       69       +2     
  Lines        9953    10105     +152     
==========================================
+ Hits         9190     9325     +135     
- Misses        763      780      +17     

Files with missing lines	Coverage Δ
src/analysis_and_optimization/Dataflow_types.ml	25.00% <100.00%> (+25.00%)	⬆️
src/analysis_and_optimization/Dataflow_utils.ml	100.00% <100.00%> (ø)
...c/analysis_and_optimization/Dependence_analysis.ml	100.00% <100.00%> (ø)
...nalysis_and_optimization/Pedantic_dist_warnings.ml	91.70% <100.00%> (ø)
src/common/Files.ml	100.00% <ø> (ø)
src/driver/Entry.ml	96.15% <100.00%> (-0.05%)	⬇️
src/driver/Flags.ml	100.00% <ø> (ø)
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)
... and 52 more

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[WardBrian]

This PR is unfortunately quite large -- if it would be easier to review module-by-module I can try out the new stacked PRs feature, but there's also no real benefit to the project until the last commit actually removing Base from the linking set is in.

Luckily almost all the changes are trivial, things like List.fold being renamed to List.fold_left, so it can also be reviewed piece by piece without keeping the whole thing in short term memory.

Let me know whichever would make your lives easier @nhuurre @SteveBronder

[WardBrian]

Ok, I don't intend to do any more history-rewriting on this branch pre-review at this point