feat!: Support invoke with structured output in OpenAI provider

[jsonbailey]

Note

Adds structured-output invokeStructuredModel with JSON schema parsing and metrics, and hardens invokeModel with try/catch and empty-content handling; comprehensive tests included.

• Server OpenAI Provider (src/OpenAIProvider.ts):
  • Structured Output: New invokeStructuredModel(messages, responseStructure) using response_format: json_schema, parses JSON payload, returns data, rawResponse, and metrics; handles missing content, JSON parse failures, and API errors with logging.
  • invokeModel: Wrapped in try/catch; derives metrics early; warns and marks failure on empty content.
  • Import StructuredResponse type.
• Tests (__tests__/OpenAIProvider.test.ts):
  • Add tests for invokeStructuredModel success, missing content, invalid JSON, and empty choices.
  • Extend invokeModel tests for empty/missing choices and metrics expectations.

^{Written by Cursor Bugbot for commit 5a3cffe. This will update automatically on new commits. Configure here.}

[github-actions]

@launchdarkly/browser size report
This is the brotli compressed size of the ESM build.
Compressed size: 169118 bytes
Compressed size limit: 200000
Uncompressed size: 789399 bytes

[github-actions]

@launchdarkly/js-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 24988 bytes
Compressed size limit: 26000
Uncompressed size: 122411 bytes

[github-actions]

@launchdarkly/js-client-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 17636 bytes
Compressed size limit: 20000
Uncompressed size: 90259 bytes

[github-actions]

@launchdarkly/js-client-sdk size report
This is the brotli compressed size of the ESM build.
Compressed size: 21721 bytes
Compressed size limit: 25000
Uncompressed size: 74698 bytes