Add type annotations and ANN lint rules

[thetic]

Summary

• Update ty from 0.0.8 to 0.0.10
• Add flake8-annotations (ANN) rules to ruff config
• Add type annotations to all config flow methods using TYPE_CHECKING guard for runtime efficiency

Test plan

• uv run ruff check passes
• uv run ty check passes
• uv run pytest passes (27 tests)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.68%. Comparing base (6ad07f9) to head (d7f63f5).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #4      +/-   ##
==========================================
- Coverage   98.68%   98.68%   -0.01%     
==========================================
  Files           6        6              
  Lines         305      304       -1     
==========================================
- Hits          301      300       -1     
  Misses          4        4              

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