[codex] BridgeJS: support associated-value enums in import and async paths

[kateinoigakukun]

Summary

• support associated-value enums in BridgeJS imported signatures instead of rejecting them in the import lowering/link paths
• allow async exported associated-value enums to use the async resolvable path
• add snapshot coverage for imported and async associated-value enum generation
• add runtime round-trip tests for imported/exported associated-value enums, including optional cases

Why

Associated-value enums already had partial support in BridgeJS, but imported signatures were still explicitly rejected and async export resolution still treated them as unsupported. That left the feature inconsistent and blocked valid enum shapes that can be passed through the stack ABI.

Validation

• swift test --package-path ./Plugins/BridgeJS --filter DiagnosticsTests
• swift test --package-path ./Plugins/BridgeJS --filter BridgeJSCodegenTests
• swift test --package-path ./Plugins/BridgeJS --filter BridgeJSLinkTests
• mise exec -- make unittest