Switch from black to ruff format

[MaxGhenis]

Summary

• Replace black with ruff for code formatting across the project
• Update dev dependencies in pyproject.toml (add ruff>=0.9.0)
• Update Makefile format target: black . -l 79 -> ruff format .
• Update CI workflows (pr.yaml, push.yaml): replace lgeiger/black-action with ruff format --check .
• Reformat all files using ruff defaults (line-length 88)

Test plan

• ruff format --check . passes
• CI lint job passes with new ruff check

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