Reduce allocations in GrpcMessageExtensionUtilities.ConvertFromHttpMessageToExpando

[kshyju]

Optimizations in GrpcMessageExtensionUtilities.ConvertFromHttpMessageToExpando method, which is a hotpath method and gets executed on every invocation in HTTP non-proxy use case.

• Removed the use of the dynamic type to build the HTTP response object, eliminating late binding and runtime dispatch.
• Replaced certain LINQ allocations.
• Using cached boxed boolean values to avoid per request boxing.
• Using a cached empty dictionary.

Improvements captured from benchmarking pipeline (Requests/sec - max) - 4 core machines.

• Windows
• Linux

Requests/sec (max)

Platform	Before	After	Delta
Linux	10,894	12,743	+16.96%
Windows	15,248	17,111	+12.21%

With this change, app handles burst traffic better. Other core metrics, such as average RPS and memory usage, have remained stable or improved slightly.

I also collected perf profiles with a local load test run which sends stable traffic (1,000 requests)

Before

Name	Total (Allocations)	Self (Allocations)	Total Size (Bytes)	Self Size (Bytes)
ConvertFromHttpMessageToExpando(RpcHttp)	85,859	3,568	4,472,970	147,112

After

Name	Total (Allocations)	Self (Allocations)	Total Size (Bytes)	Self Size (Bytes)
ConvertFromHttpMessageToExpando(RpcHttp)	15,084	3,000	763,724	184,000

Delta

• GrpcMessageExtensionUtilities.ConvertFromHttpMessageToExpando – Total allocations dropped by 70,775 (82.45%)
• GrpcMessageExtensionUtilities.ConvertFromHttpMessageToExpando – Total allocated size dropped by 3.54 MB (82.92%)

#11040 added test coverage for this code path.

Pull request checklist

IMPORTANT: Currently, changes must be backported to the in-proc branch to be included in Core Tools and non-Flex deployments.

• Backporting to the in-proc branch is not required
  • Otherwise: Link to backporting PR
• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• My changes do not require diagnostic events changes
  • Otherwise: I have added/updated all related diagnostic events and their documentation (Documentation issue linked to PR)
• I have added all required tests (Unit tests, E2E tests)