exponential backoff support

[DavidVollmers]

Traceback (most recent call last):
  File "D:\dev\GitHub\...\.venv\Lib\site-packages\big_talk\big_talk.py", line 130, in stream
    async for message in streaming_handler(ctx, **kwargs):
  File "D:\dev\GitHub\...\libs\app-common\src\app_common\middleware\conversation_history_middleware.py", line 40, in __call__
    async for message in handler(ctx, **kwargs):
  File "D:\dev\GitHub\...\libs\app-common\src\app_common\middleware\token_count_middleware.py", line 21, in __call__
    async for message in handler(ctx, **kwargs):
  File "D:\dev\GitHub\...\.venv\Lib\site-packages\big_talk\stream.py", line 36, in __call__
    async for message in ctx._stream_iteration_handler(stream_ctx, **kwargs):
  File "D:\dev\GitHub\...\.venv\Lib\site-packages\big_talk\stream_iteration.py", line 37, in __call__
    async for message in provider.stream(
  File "D:\dev\GitHub\...\.venv\Lib\site-packages\big_talk\llm\anthropic.py", line 57, in stream
    async for chunk in stream:
  File "D:\dev\GitHub\...\.venv\Lib\site-packages\anthropic\lib\streaming\_messages.py", line 215, in __aiter__
    async for item in self._iterator:
  File "D:\dev\GitHub\...\.venv\Lib\site-packages\anthropic\lib\streaming\_messages.py", line 277, in __stream__
    async for sse_event in self._raw_stream:
  File "D:\dev\GitHub\...\.venv\Lib\site-packages\anthropic\_streaming.py", line 190, in __aiter__
    async for item in self._iterator:
  File "D:\dev\GitHub\...\.venv\Lib\site-packages\anthropic\_streaming.py", line 234, in __stream__
    raise self._client._make_status_error(
anthropic.APIStatusError: {'type': 'error', 'error': {'details': None, 'type': 'overloaded_error', 'message': 'Overloaded'}, 'request_id': '...'}