feat: add LiteLLM integrations and switch demos to LiteLLM transport

[rlippmann]

what changed

• added LiteLLM SDK integration example under examples/integrations/litellm_sdk.py
• added LiteLLM proxy pre-call hook example under examples/integrations/litellm_proxy/
• added integrations index docs and linked integrations from main README/examples docs
• migrated demos transport client from OpenAI SDK to LiteLLM (demos/llm_client.py)
• updated demo dependency from openai to litellm and refreshed lockfile
• updated llm client tests for LiteLLM path and added dict-style response coverage
• bumped package version to 0.4.5

why

• provide concrete host-side LiteLLM integration examples (SDK + proxy) without changing compiler semantics
• align demo transport with LiteLLM while preserving deterministic compiler behavior and existing demo flow
• make integration paths discoverable in docs for the 0.4.5 release