smoother error handling for "message size too large" on stream

Continuing #452 and #453:

When a bot sends a message that exceeds the current [message size](https://learn.microsoft.com/en-us/microsoftteams/platform/bots/how-to/format-your-bot-messages) restriction., the service returns a 413.

Today, in the SDK, the error is just raised, with no special handling.

Doc says 403 but its actually a 413. Needs to be fixed.

**Potential considerations:**
- Raise a better error message (similiar to what we do with 403s)
- Help split the larger message into chunks

No file or test is named. Trace the SDK's stream error handling for the service's 413 response, then verify the documentation's status code and define the improved error behavior; completion should include coverage for an oversized message and a clear decision on whether chunking is in scope.

Written by the indexing model from the issue text.