make anthropic beta header usage consistent

[narengogi]

Description: (required)
-This PR makes anthropic beta header usage consistent across multiple providers (vertex, anthropic and bedrock)

• the precedence order now is header > body as it should've been all along

Type of Change:

• New feature (non-breaking change which adds functionality)

[Copilot]

Pull request overview

This PR standardizes how Anthropic beta headers (anthropic_version and anthropic_beta) are handled across multiple providers (Vertex AI, Bedrock, and Anthropic). The key improvement is establishing a consistent precedence order where header values take priority over body parameters.

Key changes:

• Modified transform functions across Vertex AI and Bedrock providers to accept providerOptions and prioritize header-sourced values
• Updated constructConfigFromRequestHeaders to extract both anthropicBeta and anthropicVersion from request headers for Bedrock and Vertex configurations
• Ensured consistent precedence: providerOptions (from headers) > body parameters > defaults

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/providers/google-vertex-ai/messages.ts	Added transform function to prioritize anthropicVersion from headers over body params
src/providers/google-vertex-ai/chatComplete.ts	Added transform function to prioritize anthropicVersion from headers over body params
src/providers/bedrock/utils/messagesUtils.ts	Updated to accept providerOptions and prioritize header values for both anthropicVersion and anthropicBeta
src/providers/bedrock/utils.ts	Updated to accept providerOptions and prioritize header values for both anthropicVersion and anthropicBeta
src/providers/bedrock/messages.ts	Updated all transform function signatures to pass providerOptions through
src/providers/bedrock/chatComplete.ts	Updated all transform function signatures to pass providerOptions through
src/handlers/handlerUtils.ts	Added extraction of anthropicVersion from headers for both Bedrock and Vertex configurations

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