010 T6: Python move to `*_test.py`; flip `-p` in the same commit; delete `tools/tests/` nf-3m0j ← Beads

Twinned from https://github.com/cfsh/ninefold/issues/1006 by tools/beads/import_github.py's reconcile pass.

From 010-co-located-tests-and-probes.md's task table (design 010). - Real dependency: T5 - Note: T1's guide states the convention (sequencing preference, not a hard dep); closes #494