Prevent OData Client sync query deadlock under UI SynchronizationContext

[Copilot]

In WinForms/WPF, synchronous LINQ execution (Where(...).ToList()) could hang even when the server responded, while ExecuteAsync completed. The sync path was waiting on async work that could resume on a blocked UI SynchronizationContext.

• Root cause

  • HttpClientRequestMessage sync response flow (GetResponse) could block while an internal async continuation attempted to marshal back to the current context.

• Client runtime change

  • Updated HttpClientRequestMessage.SendInternalAsync to avoid context capture on HttpClient.SendAsync:
    • added .ConfigureAwait(false) to the await in the send path.
  • This keeps sync callers from deadlocking when invoked from non-pumping UI contexts.

• Regression coverage

  • Added a focused test in HttpClientRequestMessageTests using a non-pumping SynchronizationContext to verify GetResponse() completes instead of hanging.

// before
return await _client.SendAsync(_requestMessage, HttpCompletionOption.ResponseHeadersRead, sendToken);

// after
return await _client.SendAsync(_requestMessage, HttpCompletionOption.ResponseHeadersRead, sendToken)
    .ConfigureAwait(false);

[nielsNocore]

was also fixed in: #3527 but ether PR would be nice to be merged. @xuzhg