fix: Preserve raw HTTP error status and bodies for non-schema errors

[darrendc26]

closes #5763

Summary

When an endpoint behind a proxy/gateway returns a non-2xx response with a body that cannot be parsed into standard SDK schemas, most providers swallow the body. This PR introduces a shared error-formatting helper to extract and surface the HTTP status and raw body from various SDK error objects instead of dropping them or returning generic errors.

Changes

• Shared Utility: Created formatProviderError in packages/ai/src/providers/error-utils.ts to inspect errors for properties like status, statusCode, $response, body, and .error, and parse stringified JSON messages (common in Google SDK errors).
• Providers: Integrated the helper in the catch blocks of:
  • amazon-bedrock.ts
  • openai-completions.ts
  • openai-responses.ts
  • azure-openai-responses.ts
  • openai-codex-responses.ts
  • google.ts
  • google-vertex.ts
  • mistral.ts
  • anthropic.ts
• Tests: Added unit tests in packages/ai/test/error-utils.test.ts to verify extraction and formatting logic across different mock provider error structures.

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