Add model attribute declaration to BaseProvider

[prudhvirapeti]

Summary

Fixes #3

• Added model: str class-level annotation to BaseProvider in skate/providers/base.py
• All provider subclasses (OpenAIProvider, AnthropicProvider, etc.) already assign self.model in __init__, but the abstract base class never declared it
• Without this declaration, type checkers like mypy cannot verify the attribute exists on the base class

Changes

One line added to skate/providers/base.py:

class BaseProvider(ABC):
    model: str  # ← added
    ...

Test plan

• pip install -e ".[dev]"
• mypy skate/providers/base.py — no errors
• pytest tests/ — all tests pass

🤖 Generated with Claude Code

[baranylcn]

Hi @prudhvirapeti, thank you for the contribution! Unfortunately #4 was opened earlier with the same change, so we're going with that one. Your PR description was excellent, please keep contributing!