fix: Prevent ObjectDisposedException in CancellationTokenSource by not disposing linked CTS

[seer-by-sentry]

This PR addresses SERVICES-54, an ObjectDisposedException occurring in CancellationTokenSource.ExecuteCallbackHandlers.

Root Cause:
The issue stemmed from a race condition in SendAsync within Constants.cs. A linked CancellationTokenSource (cts) was created with a 500ms timeout, and also linked to an externalToken (typically a 20ms tick token). The finally block attempted to disarm cts's internal timer and then dispose cts.

The ObjectDisposedException occurred when the externalToken's timer callback (running on a ThreadPool thread) attempted to cancel cts after cts had already been disposed by the finally block on the main thread. The existing try/catch (ObjectDisposedException) only protected the disposal call itself, not the concurrent callback execution.

Solution:
To eliminate this race condition, the explicit cts.Dispose() call and the associated finally block logic have been removed. The linked CancellationTokenSource is now intentionally left undisposed. Since these cts instances are short-lived and created per SendAsync operation, relying on the garbage collector to reclaim them is safe and prevents the race.

This approach ensures that when the parent token's callback fires, cts is either still active or has been safely reclaimed by the GC, thus avoiding the ObjectDisposedException.

Changes:

• Removed the finally block that contained cts.CancelAfter(Timeout.InfiniteTimeSpan) and cts.Dispose().
• Updated comments to reflect that cts is intentionally not disposed and is managed by the GC.
• Cleaned up now-redundant try/catch blocks and comments related to the old disposal logic.

Fixes SERVICES-54

[Skyaero42]

If you are not doing anything in the try/catch, you should remove it entirely - which means the parent finally block can also be removed