* chore: remove SDK struct usage from requests in messages API (#218)

Replaces MessageNewParamsWrapper that wrapped anthropic.MessageNewParams
with MessagesRequestPayload that operates on raw bytes.

* fix: remove unsupported fields from requests to Bedrock (#225)

This PR removes unsupported fields from requests to Bedrock.
Adaptive thinking field is replaced for models that don't support with `type: enabled` + `budget_tokens: N` combination.
`budget_tokens` value is calculated as a ratio of `max_tokens`.
Ratio depends on `output_config.effort` value, used the same ratio values as OpenRouter does: https://openrouter.ai/docs/guides/best-practices/reasoning-tokens#reasoning-effort-level

Fixes: https://github.com/coder/aibridge/issues/219

* fix: filter unsupported Anthropic-Beta headers from Bedrock (#226)

Removes headers from requests to Bedrock that are unsupported.

Fixes: https://github.com/coder/aibridge/issues/221