ADAP-1116: Move to hatch and pyproject.toml

[mikealfare]

We are moving to a monorepo that uses pyproject.toml and hatch. This requires a series of migrations, including this one. This PR inclues:

• update from setup.py/dev-requirements.txt to pyproject.toml/hatch.toml
• move tool config (e.g. mypy and pytest) into pyproject.toml
• update workflows regarding these moves
• delete configs that no longer apply (e.g. tox.ini, pytest.ini, etc.)

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the dbt-bigquery contributing guide.

[mikealfare]

Since integration tests are target based, and this PR updates integration tests, here's the appropriate run: https://github.com/dbt-labs/dbt-bigquery/actions/runs/11884221296

[mikealfare]

Integration tests running against the workflow from this branch:
https://github.com/dbt-labs/dbt-bigquery/actions/runs/12216250826