[Bedrock] Add strict structured-output fallback cache

[edelauna]

Which API Provider are you using?

AWS Bedrock

Which Model are you using?

Bedrock models that reject strict structured output

What happened?

Bedrock should fail soft when a model rejects strict structured output by retrying without strict mode and caching that unsupported state for a bounded TTL.

Steps to reproduce

1. Review the structured-output fallback behavior proposed in [ENHANCEMENT] Improve Amazon Bedrock support #125.
2. Add provider-specific rejection detection and retry behavior.
3. Cache unsupported strict-output state by Bedrock model or target.

Relevant API REQUEST output

N/A

Additional context

Parent issue: #124
Source PR: #125
Story point estimate: 1

Suggested PR group: PR 2 - runtime

Acceptance criteria:

• First strict-output rejection retries without strict mode.
• Subsequent requests for the same cached model/target skip strict mode while the cache entry is valid.
• Cache expiry restores the normal probe/retry behavior.
• Tests cover rejection, retry, cache hit, and cache expiry.

The current PR proposes a 30-day cache TTL; call out any desired TTL change during review.