[DNM] Fix wide-string `override_ty`#1645

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fw/arraytopointer-override-ty

Commits on Mar 6, 2026

HACK: transpile: use dashmap to enable interior mutability for `TypedAstContext::c_types`
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transpile: mint new `CTypeId`s when necessary in `TypedAstContext::type_for_kind`
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transpile: pass down modified `override_ty` for `ArrayToPointerDecay` casts
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