fix: scope CC016 awaits to their owning function

[georgepwall1991]

Summary

• stop CC016 await eligibility at nested lambda and local-function boundaries
• keep token-reference analysis capture-aware
• add a regression for a synchronous method whose only await belongs to a nested lambda
• prepare v1.27.178 release metadata

Why

The previous unrestricted descendant search made a synchronous outer method look asynchronous when only a nested function performed awaited work, producing a false unused-token diagnostic.

Validation

• red-first regression reproduced one false CC016 diagnostic
• focused CC016 tests: 10 passed
• full suite: 633 passed, 0 failed
• Release build: 0 errors (62 intentional sample analyzer warnings)
• touched-file whitespace verification: clean
• package inspection: both analyzer assemblies present; no NuGet dependencies
• self-review completed as requested; no Claude review used

Tooling note

Slopwatch is required by the local .NET overlay but unavailable on this host (command not found). Manual hygiene and exact-diff review are clean.