### Changes 🏗️
- Add OpenAI `GPT-5.2` with metadata&cost
- Add const `DEFAULT_LLM_MODEL` (set to GPT-5.2) and use it instead of
hardcoded model across llm blocks and tests
### Checklist 📋
#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
- [x] GPT-5.2 is set as default and works on llm blocks