adopt pre-commit

[2bndy5]

I noticed that this project's python sources

• do not conform to black formatting:

  circuitpython-build-tools/circuitpython_build_tools/build.py

  Line 84 in dd5f737

  if doc is None: return default

• have unused imports:

  circuitpython-build-tools/circuitpython_build_tools/scripts/build_mpy_cross.py

  Lines 28 to 29 in dd5f737

  	import os
  	import sys

  
  and unused variables:

  circuitpython-build-tools/circuitpython_build_tools/build.py

  Line 87 in dd5f737

  except (KeyError, IndexError) as e:

• have no __init__.py files, which confuses mypy and prevents proper type-checking analysis.

All of these problems can be guarded using pre-commit hooks, but they should first be addressed individually.

• Is it be desirable to address any of the above problems?
  1. If so, would adopting pre-commit be a worthwhile measure?