feat: release version 1.5.0 and improve provider registration 🚀

- **🚀 Features**
  - Improve model discovery, refresh behavior, and token counting functionality.
  - Enhance agent tools and diff handling for better model interaction.
- **🛠️ Bug Fixes**
  - Resolve tool calling failures for GPT-5.3-codex and fix 400 errors for Gemini and o1-series models.
- **🏠 Internal**
  - Refactor logging architecture and rename "LiteLLM V2" output channel to "LiteLLM Structured".
  - Implement explicit `LanguageModelChatProvider` registration in the extension activation flow.
- **📚 Docs**
  - Update README and marketplace documentation with improved quick-start instructions and pro-tips for V2 Chat features.
- **🧹 Chores**
  - Bump package version to 1.5.0.