fix(resolve): rewrite lambda signature types when merging modules

[martian56]

Problem

A named type used as a closure parameter or return type fails name resolution with cannot find \T` in scopewhen a project is built throughrvpm(package mode), even though the exact same type resolves correctly as a plain function parameter, a return type, or aletannotation. Single-fileraven build` is unaffected.

Because Raven requires closure parameters to be annotated (there is no inference for them), this blocks every higher-order library API expressed over a named type: iterator callbacks, event handlers, ORM row mappers, and so on. A consumer simply cannot write fun(x: SomeType) -> SomeType when building through rvpm.

Minimal reproduction (package mode)

// lib.rv
struct Handler { name: String }
// ...

// lib_test.rv
import "./lib" { Handler }
fun demo() {
    let f = fun(x: Handler) -> Handler = x   // error: cannot find `Handler` in scope
}

let h: Handler = ... and fun helper(h: Handler) in the same file resolve fine; only the closure signature fails.

Root cause

The stdlib expansion pass merges modules and rewrites every type annotation to its mangled, module-qualified name via rewrite_type. rewrite_fn does this for named-function parameter and return types, rewrite_stmt does it for let annotations, and struct/enum/const/impl are all covered. The rewrite_expr ExprKind::Lambda arm rewrote only the lambda body, never its parameter or return type annotations, so those kept the bare name that no longer exists in the merged module scope.

Fix

Rewrite the lambda parameter and return type annotations with the full rename map in the ExprKind::Lambda arm, mirroring rewrite_fn. Value parameters still shadow only globals in the body, so the annotations correctly use the unshadowed map.

Tests

• New regression test lambda_parameter_type_from_merged_module_resolves in src/resolve/stdlib.rs: a lambda whose parameter and return type come from a merged module now expands, resolves, type-checks, and lowers.
• Full suite green locally: 685 lib tests plus all integration suites, 0 failures.

Summary by CodeRabbit

• Bug Fixes
  • Fixed unresolved type references in lambda parameter and return type annotations when modules are merged.
  • Lambda expressions now correctly resolve, type-check, and compile when their annotations refer to types from another module.