chore: clean up dependencies

[ajbozarth]

Clean up and organize the dependencies, optional dependencies, and dependency groups to follow a clear pattern:

1. dependencies - Core packages required at runtime (always installed)

   • Use for: Essential functionality everyone needs

2. project.optional-dependencies - Optional feature groups users can choose

   • Use for: Optional backends, integrations, heavy dependencies
   • Install with: pip install package[feature]

3. dependency-groups - Development workflow dependencies

   • Use for: Testing, linting, docs (dev-only, not in package distribution)
   • Install with: uv sync --group test
   • Key benefit: Cleaner separation, not included in published package metadata

Decision Guide

• Runtime required → dependencies
• Optional user feature → project.optional-dependencies
• Development only → dependency-groups

The key insight: dependency-groups is the modern standard for development dependencies that shouldn't be part of your package's public API, while optional-dependencies is for user-facing optional features.