Add opt-in cross-module inlining for Option helpers

[cknitt]

Add @inline(crossModule) to opt individual functions into cross-module inlining, and use it for selected Option helpers.

Inlining copies a function’s body into its callers. If that body changes but its type does not, the caller must still be rebuilt; checking only the .cmi type signature would leave the old body in the generated JavaScript.

The compiler stores exported inline bodies in the existing .cmj file, alongside other JavaScript compilation metadata. Rewatch now compares the digest already stored in that file’s header before and after compiling a module. If it changes, Rewatch rebuilds dependents. This keeps implementation details out of .cmi and requires no new artifact. A .cmj change unrelated to inlining may also cause a dependent rebuild.

[codecov]

Codecov Report

❌ Patch coverage is 57.89474% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.71%. Comparing base (ece8b14) to head (24646c5).

Files with missing lines	Patch %	Lines
compiler/ml/translattribute.ml	66.66%	3 Missing ⚠️
compiler/core/lam_stats_export.ml	66.66%	2 Missing ⚠️
compiler/ml/printlambda.ml	0.00%	2 Missing ⚠️
compiler/core/lam_analysis.ml	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8689      +/-   ##
==========================================
+ Coverage   78.67%   78.71%   +0.03%     
==========================================
  Files         476      476              
  Lines       64402    64413      +11     
==========================================
+ Hits        50670    50704      +34     
+ Misses      13732    13709      -23     

Files with missing lines	Coverage Δ
compiler/core/js_cmj_format.ml	92.72% <100.00%> (+0.13%)	⬆️
compiler/ml/lambda.ml	64.89% <ø> (ø)
compiler/core/lam_analysis.ml	65.92% <0.00%> (-0.75%)	⬇️
compiler/core/lam_stats_export.ml	88.23% <66.66%> (-2.88%)	⬇️
compiler/ml/printlambda.ml	9.33% <0.00%> (-0.08%)	⬇️
compiler/ml/translattribute.ml	78.78% <66.66%> (+0.66%)	⬆️

... and 7 files with indirect coverage changes

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commit: 24646c5

[github-actions]

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Treat catch binders as local during inline validation

For an exported @inline(crossModule) function containing a try ... catch whose handler inspects the exception, this check incorrectly rejects the function as capturing a local value. Lam_closure.is_closed delegates to free_variables, but its Ltrywith branch ignores _exn instead of adding that binder to the local set (compiler/core/lam_closure.ml:118-120), so ordinary references to the caught exception are reported as free. Register the catch binder during closure traversal or use validation that handles all Lambda binders.

AGENTS.md reference: AGENTS.md:L51-L54

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