Fix Result<T, E> type mismatch when E is a user enum

[Cod-e-Codes]

Summary

• resolve_type_name rewrites parser Struct names to Enum inside generic parameters (and other composite types), so Result<int, MyError> from a return type equals Result::Err(MyError::Bad).
• Previously expected and actual printed identically (expected Result<int, MyError>, got Result<int, MyError>).
• Integration test imports stdlib/result.ion and covers Ok, Err, and match; unit test uses a local Result to isolate substitution from imports.

Test plan

• cargo fmt, clippy -D warnings, cargo test
• tests/test_runner.sh (273/273)
• Example ion-build for all 14 examples; non-interactive examples run