feat(cache): add TTL support to CachePoint for prompt caching

[kpx-dev]

Description

Add optional ttl field to CachePoint TypedDict to support AWS Bedrock's cache TTL configuration. The field accepts "5m" or "1h" values as specified in the Bedrock API. Updated BedrockModel to preserve ttl field when formatting cache point content blocks. Includes tests for TTL preservation and backward compatibility.

Doc shows API supports ttl option now:
https://docs.aws.amazon.com/bedrock/latest/APIReference/API_runtime_CachePointBlock.html

launch announcement:
https://aws.amazon.com/about-aws/whats-new/2026/01/amazon-bedrock-one-hour-duration-prompt-caching/

more details:
https://docs.aws.amazon.com/bedrock/latest/userguide/prompt-caching.html

Related Issues

#1243

Documentation PR

Type of Change

New feature

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

• [x ] I ran hatch run prepare

Checklist

• [x ] I have read the CONTRIBUTING document
• [ x] I have added any necessary tests that prove my fix is effective or my feature works
• [x ] I have updated the documentation accordingly
• [ x] I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• [x ] My changes generate no new warnings
• [ x] Any dependent changes have been merged and published

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