fix: Add token counting functionality and update agent tools

This commit introduces the ability to count tokens using LiteLLM's API and updates the tools available to the investigative agent.

✨ Features
- Implement token counting functionality using the LiteLLM API. This allows for more accurate token estimation by leveraging the LiteLLM proxy's capabilities.

🧹 Chores
- Update the investigative agent's tool list to include new capabilities like `vscode/memory`, `browser/openBrowserPage`, `web/githubRepo`, and various `github.vscode-pull-request-github` tools. This enhances the agent's ability to gather information and interact with GitHub.
- Increment the package version from `1.4.3-dev5` to `1.4.3-dev6`.
- Update `llm-response.json` with a comprehensive list of new and updated model configurations, including various Anthropic, OpenAI, and Vertex AI models with their respective parameters and costs. This ensures the system is aware of and can utilize a wider range of LLM providers.