[plugins] port Amazon Bedrock to Go

[cabljac]

Port of the Amazon Bedrock plugin to Go.

This builds on the existing genkit-ai/aws-bedrock-go-plugin repo. Scope and ordering were agreed upstream in the discussion issue:

➡️ Tracking discussion: genkit-ai/aws-bedrock-go-plugin#136

Work is landing as small, focused PRs, one per section:

• 1. Mechanical file split (no behaviour changes) — refactor(bedrock): split bedrock plugin implementation by concern aws-bedrock-go-plugin#140
• 2. Reranking — feat(rerank): add Bedrock reranking support aws-bedrock-go-plugin#141
• 3. Bedrock reasoning support — feat: add Bedrock reasoning support aws-bedrock-go-plugin#142
• 4. Broader embeddings (Titan / Cohere / Nova text, image, multimodal)
• 5. Richer per-call config surface
• 6. Tool choice wiring
• 7. More complete Converse request/response conversion
• 8. Streaming reassembly
• 9. Model capability registry & inference profiles
• 10. Image generation across more families
• 11. AWS config & region resolution
• 12. Expanded unit tests
• 13. Opt-in live-test matrix
• 14. README & examples refresh

[adesinah]

PR:
#5440

[apascal07]

We have an existing plugin built by @xavidop here: https://github.com/genkit-ai/aws-bedrock-go-plugin