Add prompt caching support for AWS Bedrock

[DenysMoskalenko]

Summary

Implements AWS Bedrock prompt caching support (see #3418) by fixing how cache points are sent, documenting the workflow, and extending test coverage to assert cache writes and reads.

Testing

• uv run pytest tests/models/test_bedrock.py
• uv run coverage run -m pytest tests/models/test_bedrock.py

[DenysMoskalenko]

@DouweM It's mostly the duplication of the same documentation we have for Anthropic CachePoint. What do you think, maybe we need to move it somewhere?

[DenysMoskalenko]

@DouweM Is there any change to continue with this PR? We need this feature a lot 🙏.

I read the #3453 but I guess that we can add bedrock support in the same way and make changes later for both places if needed, instead of just ignoring the Bedrock users. What do you think?

[DouweM]

@DenysMoskalenko Thanks for working on this Denys!

I guess that we can add bedrock support in the same way and make changes later for both places if needed, instead of just ignoring the Bedrock users. What do you think?

Agreed. Can you please have a look at these issues and address them in case they affect this implementation as well?

• Add ttl to CachePoint and Anthropic caching model settings #3450
• Anthropic prompt caching fails when there are more than 4 cache points #3467
• Also see the last comment on Enable more advanced Anthropic prompt caching than CachePoint implementation llows #3453 where it was said that Amazon Nova may need special consideration.
• Related to that last one, it's also worth checking what happens when a cache point is sent to a non-Anthropic model. If that's not supported, we should make sure we send them only to Anthropic models using a new flag on BedrockModelProfile (there are some examples in the file already)