Test: ignore inferred arity in case of %raw.

[cristianoc]

The inferred arity of raw JS code is actively used with %ffi, but it can produce unexpected results with %raw:

let foo: int => int = %raw(`function add(x, y=5){ return x + y }`)

Console.log(foo(2))

This PR tests turning off the use of inferred arity so that int => int above is just taken at face value.

[Copilot]

Pull Request Overview

This PR disables the compiler’s automatic arity inference for raw JavaScript code by preventing the existing pattern branches from matching.

• Added when false guards to skip raw JS arity collection in lam_pass_collect.ml
• Added when false guards to skip raw JS arity analysis in lam_arity_analysis.ml

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
compiler/core/lam_pass_collect.ml	Disabled inferred arity collection for %raw by guarding the JS function pattern with when false
compiler/core/lam_arity_analysis.ml	Disabled inferred arity analysis for %raw by guarding the JS function pattern with when false

[Copilot]

[nitpick] Using a when false guard makes this branch permanently unreachable. Consider removing the dead code or replacing the guard with a named feature flag and an explanatory comment to clarify intent.

[Copilot]

[nitpick] This when false guard disables the raw JS arity branch but leaves dead code. It may be clearer to remove the branch or use a descriptive compile‐time flag plus comments to document why it's disabled.

Suggested change

	when false ->
	Lam_arity.info [arity] false
	when ENABLE_RAW_JS_ARITY ->
	Lam_arity.info [arity] false
	(* The ENABLE_RAW_JS_ARITY flag controls whether the raw JS arity branch is enabled.
	This branch is currently disabled for performance reasons and because it is not
	required in the current implementation. Enable it by defining ENABLE_RAW_JS_ARITY
	as true at compile time if needed in the future. *)

[tsnobip]

@cristianoc this means inferred arity will be ignored even when there's no type signature, right? It's dangerous anyway since it doesn't reflect it in the types.
I guess you can still use %ffi if you want to type your js code. We should likely document %ffi by the way.