test: Add comprehensive edge case tests for Ollama embedding and chat models

[alxkm]

Adds comprehensive test coverage for edge cases and boundary conditions in Ollama model implementations:

OllamaEmbeddingRequestTests:

• Null input handling in embedding requests
• Partial options override behavior (ensures defaults are preserved when not explicitly overridden)
• Empty string input processing

OllamaChatModelTests:

• Minimal value handling in chat response metadata
• Minimal configuration model building

These tests improve robustness by validating behavior with edge cases like null/empty inputs, partial configuration overrides, and boundary values that could occur in production environments.

[sobychacko]

Merged via 5b195a4.