Handle function application in rewrite checker

[nskh]

Allows us to rewrite-check things like f(x) + 1 being equivalent to 1 + f(x); all we have to do is unpack function application. Even works when f, x have not been defined:

Closes #1842.

[Copilot]

Pull Request Overview

This PR enhances the rewrite checker to handle function application expressions, enabling equivalence checking for expressions like f(x) + 1 and 1 + f(x). The change allows the system to unpack and properly represent function applications even when the function and arguments are undefined.

• Adds support for function application (Ap) pattern matching in the algebrite expression printer
• Improves debugging output for unknown expression types with detailed logging
• Updates a TODO comment attribution

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[Copilot]

Adding debug output via print_endline in production code can clutter console output and may not be appropriate for all environments. Consider using a proper logging mechanism or making this conditional based on a debug flag.

Suggested change

	);
	if (debug) {
	print_endline(
	"Algebrite rewrite checker received unknown value of type "
	++ Exp.show(exp),
	);
	};

[codecov]

Codecov Report

❌ Patch coverage is 0% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.68%. Comparing base (3636f8c) to head (c135936).

Files with missing lines	Patch %	Lines
src/web/app/editors/stepper/RewriteChecker.re	0.00%	22 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1877      +/-   ##
==========================================
- Coverage   50.79%   50.68%   -0.11%     
==========================================
  Files         204      204              
  Lines       21355    21376      +21     
==========================================
- Hits        10847    10835      -12     
- Misses      10508    10541      +33     

Files with missing lines	Coverage Δ
src/web/app/editors/stepper/RewriteChecker.re	0.00% <0.00%> (ø)

... and 13 files with indirect coverage changes

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[Negabinary]

Had a play with it; these are some examples I'd prefer if they gave the opposite answer

[nskh]

Fixed length (builtins) and list concat handling. Still working on the function stuff, we may need to chat about how to handle those generally.