Fix flaky HTTP request logger test

[Widthdom]

Summary

• Extended the HTTP MCP request logger test grace period for async log delivery under full-suite load.
• Added timeout diagnostics that show the request log records observed before failure.

Validation

• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --filter FullyQualifiedName~HttpMcpTransportTests
• dotnet run --project tools/CodeIndex.Changelog -- check
• git diff --check

Full dotnet test was attempted, but an unrelated trimmed publish test failed because ILLink could not write src/CodeIndex/obj/Debug/net8.0/osx-arm64/linked/cdidx.pdb while another process held it.

Documentation and changelog

• Added changelog fragment changelog.d/unreleased/2419.fixed.md.
• No documentation update needed; this is a test stability fix only.

Adversarial review

• Manual adversarial review found no blocking/actionable issues.
• Codex adversarial review was attempted, but the usable diff-based run was blocked by the Codex usage limit.

Fixes #2419