v0.17.0: Add LLM package with support for multiple providers and output formats

- Introduced `llm` package for Large Language Model operations.
- Implemented support for OpenAI, Gemini, and Vertex AI providers.
- Added model options and interfaces for flexible configuration.
- Included various output formats: text, JSON, XML, YAML, and image formats.
- Created mock model for testing purposes.
- Added comprehensive tests for model creation and completion functionality.
- Updated go.mod and go.sum with necessary dependencies.