Fix terminal primitive array get returns

[luisleo526]

Summary

• preserve exact primitive return types when an ordinary UDF ends in a supported direct array.get(...) or receiver.get(...)
• cache the exact return TypeSpec so downstream collection inference does not revisit stateful calls and mint extra call-site state
• keep the change deliberately bounded to exact identifier-backed arrays and primitive elements; temporary receivers, UDT/reference-like elements, nested collections, extensions, matrix/range/view semantics, and unresolved parameters remain unchanged

Why

The analyzer already knew the array element TypeSpec, but its coarse array-method visitor returned VOID. The function analyzer discarded the exact terminal element spec, so codegen fell back to double. String returns failed C++ compilation, while integer returns often compiled and silently masked the defect. Re-inferring the terminal expression later could also duplicate stateful call sites.

Verification

• focused and adjacent array suites: 76/76 passed with the engine include enabled
• full Python suite: 1745 passed, 2 skipped
• browser/Pyodide gate: 8 comparator and 10 verdict cases passed
• full codegen gate: 277 fixtures, 263 expected-success passed, 14 expected-error passed, parity passed
• exhaustive publication matrix: 2^5 = 32/32 expected outcomes across base/candidate, functional/member form, local/declared parameter, int/string, and direct/stateful nested consumer
• full standard-corpus sweep: 415 classified; 408 transpile OK; public board remained Excellent 352 / Strong 47 / Moderate 4 / Weak 3; 0 upgrades and 0 downgrades
• causal artifact audit: no generated-C++ or engine-trade semantic hash changed for any graded row