v0.3.0

Add Cohere provider and fix test suite

• Add Cohere client with multimodal and structured output support

  • Implement CohereClient with vision model support (command-a-vision)
  • Add pricing data for command-r, command-r-plus, command-r7b, command-a models
  • Create comprehensive unit and integration tests
  • Add example_cohere.py demonstrating usage

• Fix base_url configuration for OpenRouter and sciCORE

  • Set default base_url before client instantiation instead of after
  • Ensures SDK clients are initialized with correct endpoints

• Fix test suite Mock comparison errors

  • Add isinstance() checks before comparing potential Mock objects with integers
  • Update mock fixtures to include cache-related attributes
  • Fix mock patching paths to use import locations (ai_client..)
  • Correct conversation continuation test expectation