GeezerVison

Add a basic bedrock extension that creates chat spans with the gen_ai.operation.name, gen_ai.provider.name and gen_ai.response.streaming attributes.

This is the first boto3 extension. I've cleaned up some things:

• Remove registry.py. We control all extensions in the SDK, so this indirection seems unnecessary.
• Related to the above, remove tests for the registry system that define mock extensions. Create success and error test cases in test_bedrock.py so the relevant behavior is still exercised.
• Remove capture_internal_exceptions() around invocations of extension functions. If there's code that can raise in the extensions, the extensions can wrap the relevant lines themselves.
• Add a skip_if_no_active_span boolean so that Bedrock spans are created even when there is no active span, matching the behavior of other chat integrations.