[macOS] LargeUriAndHeaders_Works times out

## Build Information

Build: https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_build/results?buildId=1586600

Build error leg or test failing: `System.Net.Http.Functional.Tests.WorkItemExecution - LargeUriAndHeaders_Works`

Pull request: https://github.com/dotnet/runtime/pull/133391

## Error Message

```json
{
"ErrorMessage": [
"HttpClientHandlerTest.LargeUriAndHeaders_Works [FAIL]",
"System.TimeoutException : The operation has timed out."
],
"ErrorPattern": "",
"BuildRetry": false,
"ExcludeConsoleLog": false
}
```

## Failure Details

```text
System.Net.Http.Functional.Tests.SyncHttpHandler_HttpClientHandlerTest.LargeUriAndHeaders_Works [FAIL]
System.TimeoutException : The operation has timed out.
Stack Trace:
/_/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.cs(2357,0): at System.Net.Http.Functional.Tests.HttpClientHandlerTest.LargeUriAndHeaders_Works()

System.Net.Http.Functional.Tests.SocketsHttpHandler_HttpClientHandlerTest.LargeUriAndHeaders_Works [FAIL]
System.TimeoutException : The operation has timed out.
Stack Trace:
/_/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.cs(2357,0): at System.Net.Http.Functional.Tests.HttpClientHandlerTest.LargeUriAndHeaders_Works()
```

Failing configuration:

`net10.0-osx-Debug-x64-coreclr_release-OSX.15.Amd64.Open`

The test sends a 10,000,000-character URI path, header name, and header value
through a local loopback server. The work item failed on all three Helix
attempts: the synchronous handler timed out on every attempt and
SocketsHttpHandler timed out on two attempts.

Previous platform-specific failures were tracked by #117942 for WebAssembly and
#124487 for Android. Those issues were closed after platform-specific test
changes and do not cover this macOS failure.

Console log:
https://helixr1107v0xdeko0k025g8.blob.core.windows.net/dotnet-runtime-refs-pull-133391-merge-b62c8f5a996540b5a0/System.Net.Http.Functional.Tests/3/console.d8f46254.log?helixlogtype=result

### Known issue validation
**Build: :mag_right:** https://dev.azure.com/dnceng-public/public/_build/results?buildId=1586600
**Error message validated:** `[HttpClientHandlerTest.LargeUriAndHeaders_Works [FAIL] System.TimeoutException : The operation has timed out.`]
**Result validation:** :white_check_mark: Known issue matched with the provided build.
**Validation performed at:** 9/11/2026 6:27:00 PM UTC

### Report

|Build|Repository|Test|Pull Request|
|---|---|---|---|
|[1586600](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1586600)|dotnet/runtime|[System.Net.Http.Functional.Tests.SyncHttpHandler_HttpClientHandlerTest.LargeUriAndHeaders_Works](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1586600&view=ms.vss-test-web.build-test-results-tab&runId=43782190&resultId=224789)|dotnet/runtime#133391|
#### Summary
|24-Hour Hit Count|7-Day Hit Count|1-Month Count|
|---|---|---|
|0|0|1|

Start with src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.cs at line 2357 and run LargeUriAndHeaders_Works on the net10.0-osx Debug x64 configuration. Compare the synchronous and SocketsHttpHandler failures with the linked build and console log to isolate the macOS timeout. Done means the test no longer times out on macOS and the relevant test coverage or platform handling is validated.

Written by the indexing model from the issue text.