Retry on throttle and quota errors in integ test

[Alan4506]

Description of changes:

The test_get_medical_scribe_stream integration test previously only retried on BadRequestException (IAM role propagation delay). When multiple test runs execute concurrently against the same account, the test can also encounter:

• LimitExceededException: post-stream analytics job quota exceeded
• ThrottlingException (surfaced as CallError): concurrent streaming session limit exceeded

This change adds retry handling for both cases. The ThrottlingException is not modeled in the service's error registry, so it arrives as a generic CallError, and we match it by error id in the message string.

Testing:

Without these changes, running 20 concurrent instances of integration tests:

for i in $(seq 1 20); do python -m pytest tests/integration/ -s & done; wait

results in failures with LimitExceededException and CallError: Unknown error ... ThrottlingException. With the fix applied, 20/20 concurrent runs pass.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.