[lindicaphxag-tech]

Closes #806

LiteLLMClient currently creates a disk cache at module import time, so the cache directory cannot be selected from a model configuration.

This adds an optional litellm_cache_dir to LiteLLMModelConfig. When it is set, the client configures LiteLLM's disk cache with that directory; leaving it unset keeps the existing default behavior. The example config and focused unit coverage are included.

Validation:

• Python compilation of the changed module and test file
• Isolated config/cache initialization test with a stubbed LiteLLM cache

[lindicaphxag-tech]

Following up on #806: the optional litellm_cache_dir keeps the existing default when omitted, and the PR includes focused cache-initialization coverage plus an example config. Could a maintainer review when available and flag any compatibility concerns with LiteLLM cache initialization?