Add Docker integration example for Provably with Model Runner

[SimoneBottoni]

This pull request adds a new example demonstrating how to integrate Provably with a locally running LLM via Docker Model Runner. The example includes documentation, environment variable configuration, and a runnable agent script that fetches weather data, runs a local LLM, and evaluates the result with Provably. The most important changes are grouped below:

New Local Model Example:

• Added examples/local_model/README.md with step-by-step instructions for running a local LLM with Provably, including setup for Docker Model Runner, environment variables, and PostgreSQL requirements.
• Added examples/local_model/.env.example providing sample environment variables for configuring Provably, Docker Model Runner, and PostgreSQL.
• Added examples/local_model/agent_run.py, a runnable Python script that demonstrates fetching weather data, intercepting the response, running a local LLM, and evaluating the result with Provably, including an option to simulate a hallucinated response.