#20866: fix: disable prompt caching for non-Anthropic Bedrock models

When using non-Anthropic models on Bedrock (like Amazon Nova or Mistral), the upstream pi-ai provider injects `cachePoint` blocks into message content by default. These models don't support the Anthropic-specific cache point extension and reject requests with 'extraneous key [cachePoint] is not permitted'. This passes `cacheRetention: "none"` to the pi-ai stream options for non-Anthropic Bedrock models, which prevents cachePoint blocks from being added in the first place. Anthropic models on Bedrock are unaffected and keep their existing caching behavior. Fixes #20815 <!-- greptile_comment --> <h3>Greptile Summary</h3> Fixes Bedrock API errors when using non-Anthropic models (Amazon Nova, Mistral) by disabling prompt caching for them. The pi-ai Bedrock provider injects `cachePoint` blocks by default, but only Claude models support this Anthropic-specific extension. The fix adds a detection function to identify Claude model IDs (matching `anthropic.claude` or `anthropic/claude`) and wraps the stream function to pass `cacheRetention: "none"` for all other Bedrock models. This prevents the upstream provider from injecting unsupported cache control metadata that would cause API rejection errors. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk - The fix is narrowly scoped, well-documented, and follows existing patterns in the codebase. The detection logic correctly identifies Anthropic models using case-insensitive string matching, and the wrapper correctly chains with existing streamFn wrappers. No tests need updating since this is defensive behavior that prevents errors rather than changing existing functionality. - No files require special attention _{Last reviewed commit: 2302126} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->