refactor: Always return ModelInfo instance

[tymondesigns]

This pull request introduces significant updates to the Cortex\ModelInfo library, focusing on improving type safety, adding metadata support, and enhancing provider implementations. Key changes include replacing string-based model representations with a ModelInfo class, introducing metadata for models, and updating multiple providers to use the new structure.

Enhancements to Model Representation:

• Updated ModelInfo class to include an optional metadata field and corresponding getMetadata method for retrieving metadata by key. Adjusted constructor to allow nullable cost fields (inputCostPerToken and outputCostPerToken). [1] [2]
• Refactored ModelInfoProvider interface and related implementations (LiteLLMModelInfoProvider, LMStudioModelInfoProvider, OllamaModelInfoProvider) to return ModelInfo objects instead of strings, ensuring type safety. [1] [2] [3] [4]

Provider-Specific Improvements:

• Added a new LMStudioModelInfoProvider to the default providers in ModelInfoFactory.
• Enhanced OllamaModelInfoProvider and LiteLLMModelInfoProvider to map responses into ModelInfo objects, improving consistency and extensibility. [1] [2]
• Updated LMStudioModelInfoProvider and OllamaModelInfoProvider to handle new metadata and improve response handling. [1] [2]

Enum and Type Updates:

• Renamed the ModelType::Other enum case to ModelType::Unknown for clarity.
• Adjusted ModelProvider methods to return ModelInfo objects instead of strings, aligning with the updated interface. [1] [2]

Documentation and Tests:

• Updated PHPStan type definitions across the codebase to reflect the new ModelInfo structure and metadata support. [1] [2]
• Added test coverage for metadata handling in ModelInfoFactoryTest.

These changes collectively improve the library's type safety, extensibility, and ability to handle richer model metadata.