linting, type safety, and CI pipeline

[domino-blake]

What does this PR do?

Adds automated quality gates and cleans up all pre-existing violations — no user-facing API changes.

CI / tooling

• Adds .github/workflows/ci.yml with three gating jobs: lint (black, isort, flake8,
  snake_case check), typecheck (mypy), and test (pytest matrix across Python 3.10/3.11/3.12)
• Adds scripts/check_snake_case.py — an AST-based checker that prevents new camelCase
  public parameter names from being introduced
• Rewrites tox.ini to cover all supported Python versions
• Updates all pre-commit hook versions to current releases
• Adds pyproject.toml with isort/black config

Type safety

• Resolves all 38 pre-existing mypy errors across 9 files (domino/domino.py,
  domino/datasets.py, domino/_custom_metrics.py, domino/airflow/_operator.py,
  domino/agents/)

Formatting

• Resolves all flake8, isort, and black violations across the codebase

Testing

• 188 unit tests pass, 55 skipped (require live Domino deployment)

• All pre-commit checks pass: black, isort, flake8, check_snake_case, mypy

• Unit tests passing

• No user-facing API changes

• CI jobs validated locally

---

[ddl-bira-ignacio]

Nice tidying up. Given the new quality enforcement steps here, we might want to add to the docs how devs can detect those failures locally and, for things that can be auto fixed with linting tools, how to run them.