DEV: Update pre-commit stack and fix executable files

[scottclowe]

• Remove executable flag from unexecutable files. I think the flag was wrong because the files were originally committed on Windows?
• Add executable flag to setup.py
• Migrate from black_nbconvert to nbqa-black, which is actively maintained and has a release that supports cell magic
• Add new hooks from pre-commit/pygrep-hooks
• Add new hooks from pre-commit/pre-commit-hooks

[codecov]

Codecov Report

Merging #234 (bf88326) into master (91b9c91) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #234   +/-   ##
=======================================
  Coverage   92.75%   92.75%           
=======================================
  Files           8        8           
  Lines         939      939           
  Branches      197      197           
=======================================
  Hits          871      871           
  Misses         33       33           
  Partials       35       35           

Flag	Coverage Δ
nbsmoke	66.02% <ø> (ø)
unittests	92.33% <ø> (ø)

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Impacted Files	Coverage Δ
fissa/extraction.py	95.04% <ø> (ø)
fissa/neuropil.py	91.66% <ø> (ø)

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