chore(py_pytest_main): Refactor to allow for linting

[arrdem]

The pytest driver template isn't valid Python, which makes it unlintable, which is part of why it has unmitigated typing issues which become visible when users adopt rules_mypy and equivalents.

Rework the driver template so that in its pre-expansion form it's valid Python and impose linting on it.

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Changes are visible to end-users: no

Test plan

TBD

[aspect-workflows]

Test

All tests were cache hits

35 tests (100.0%) were fully cached saving 1m 3s.

[github-actions]

e2e/use_release folder: LCOV of commit c261808 during CI #1796

Summary coverage rate:
  lines......: 100.0% (2 of 2 lines)
  functions..: 100.0% (1 of 1 function)
  branches...: no data found

Files changed coverage rate: n/a