feat(translator): enhance request and response parsing for Gemini API and CLI
- Added support for removing predefined JSON paths (`additionalProperties`, `$schema`, `ref`) during request transformation for Gemini.
- Introduced `FunctionIndex` parameter to manage function call indexing in streaming responses for both API and CLI translators.
- Improved handling of tool call content and function call templates in response parsing logic.
- Added `examples/custom-provider/main.go` showcasing custom executor and translator integration using the SDK.
- Removed redundant debug logs from translator modules to enhance code cleanliness.
- Updated SDK documentation with new usage and advanced examples.
- Expanded the management API with new endpoints, including request logging and GPT-5 Codex features.
- Renamed `openai` packages to `chat_completions` across translator modules.
- Introduced `openai_responses_handlers` with handlers for `/v1/models` and OpenAI-compatible chat completions endpoints.
- Updated constants and registry identifiers for OpenAI response type.
- Simplified request/response conversions and added detailed retry/error handling.
- Added `golang.org/x/crypto` for additional cryptographic functions.
