Use ruff formatter, introduce helper dev script

[arjkesh]

Description

1. Format files with https://pypi.org/project/ruff/
2. Add helper script for users to run ruff with project specifications
3. Update PR template documentation
4. Updates GH actions checker

Important files

• pyproject.toml: moved from darker to ruff
• .github/workflows/tilegym-ci-infra-tests.yml: update to use ruff
• format.sh: dev script

CI Configuration

config:
  build: true
  # valid options are "ops" and "benchmark"
  test: ["ops", "benchmark"]

Checklist

• Documentation updated (if needed)
• CI configuration reviewed

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[arjkesh]

/ok to test 278b5da

[hannahli-nv]

LGTM, thx!