fix(codegen): infer terminal map UDF returns

[luisleo526]

Summary

• infer direct terminal map UDF returns for void, collection, and string-valued methods
• support functional, global, local, typed-parameter, and call-site-inferred parameter forms
• preserve ordinary keyword/arbitrary-receiver routing, invalid-source behavior, nonterminal output, and shared map runtime semantics

Validation

• focused pinned-engine matrix: 9 passed
• full pinned-engine suite: 1717 passed, 2 skipped
• Pyodide gate: 277/277 parity
• 666-source manifest: byte-identical to baseline, 660 OK and the same 6 errors
• adversarial residual parity: 15/15 baseline-identical
• N=2 hidden-factor matrix: no base-pass to candidate-fail cell

Follow-up

A pre-existing cross-function raw-name TypeSpec collision remains isolated for the next campaign lane; it is not introduced by this patch.