Add safety check for bedrock ConverseStream responses

[liustve]

Description

Add defensive check for Bedrock responses missing expected structure. When no messageStart event with assistant role is received, the response may lack the standard output.message format, causing the occasional KeyError exceptions.

Fixes #3958

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

I was unable to reproduce the exact scenario that would trigger this bug , this safety check would fix this without affecting normal instrumentation behavior.

Does This PR Require a Core Repo Change?

• [x ] No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[xrmx]

@liustve Please fix the CI failures and next time please run the tests locally :)

[xrmx]

@liustve I don't think you pushed a fix for the test:

_____________ test_converse_stream_with_missing_output_in_response _____________

    def test_converse_stream_with_missing_output_in_response():
        """Test that converse stream handles malformed response missing output key."""
    
        def stream_done_callback(response, ended):
            pass
    
>       wrapper = ConverseStreamWrapper(
            stream=mock.MagicMock(),
            stream_done_callback=stream_done_callback,
            model_id="amazon.nova-micro-v1:0",
        )
E       TypeError: ConverseStreamWrapper.__init__() got an unexpected keyword argument 'model_id'

instrumentation/opentelemetry-instrumentation-botocore/tests/test_botocore_bedrock.py:3061: TypeError

[liustve]

@liustve I don't think you pushed a fix for the test:

_____________ test_converse_stream_with_missing_output_in_response _____________

    def test_converse_stream_with_missing_output_in_response():
        """Test that converse stream handles malformed response missing output key."""
    
        def stream_done_callback(response, ended):
            pass
    
>       wrapper = ConverseStreamWrapper(
            stream=mock.MagicMock(),
            stream_done_callback=stream_done_callback,
            model_id="amazon.nova-micro-v1:0",
        )
E       TypeError: ConverseStreamWrapper.__init__() got an unexpected keyword argument 'model_id'

instrumentation/opentelemetry-instrumentation-botocore/tests/test_botocore_bedrock.py:3061: TypeError

Apologies, had to fix a few things in my local dev environment, for some reason the tests were using another version of OTel botocore.

Also revised the test to better capture the intended behavior.

[liustve]

@xrmx added another defensive check for orig_message["content"] as well. Just in case.