fix: reject nameof as context token observation

[georgepwall1991]

Verdict

CC020 and CC021 now keep reporting when a gRPC or HTTP context token property appears only inside nameof(...); compile-time metadata does not observe request cancellation at runtime.

Evidence

• Red-first regressions reproduced both false negatives: expected one diagnostic, actual zero.
• The shared AccessesMember helper now excludes member accesses nested under INameOfOperation.
• Real direct, alias, method-call, and forwarded-context observations remain covered and green.
• Release build: 62 intentional sample diagnostics, 0 errors.
• Tests: 638 passed, 0 failed.
• Touched-file whitespace verification passed.
• NuGet package v1.27.181 contains both analyzer assemblies and no dependency groups.
• Self-review: no actionable findings.
• Slopwatch was attempted after code changes but is unavailable on this host (command not found).
• Per explicit instruction, no Claude review was used.

Next action

Merge after required CI passes, then publish and verify v1.27.181.