apply black formatting

[tlambert03]

This PR would enable code formatting with black.

This would complete what I think are three most useful linting components:

1. ruff (linting, import sorting, style enforcement, and some autofixes of best practices) #6
2. mypy (static type checking) #5
3. black (this PR) which formats code, standardizing how the code base "looks" even if you have multiple contributors. It has some configurability if you want, but the defaults are reasonable.

@funkey, have a look at what it did here, and let me know if have opinions on any of the stylistic changes (they might be configurable)

[codecov-commenter]

Codecov Report

Merging #11 (ec4da88) into main (54853ac) will not change coverage. The diff coverage is 83.33%.

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@@           Coverage Diff           @@
##             main      #11   +/-   ##
=======================================
  Coverage   85.64%   85.64%           
=======================================
  Files          27       27           
  Lines         613      613           
=======================================
  Hits          525      525           
  Misses         88       88           

Impacted Files	Coverage Δ
motile/constraints/max_children.py	95.23% <ø> (ø)
motile/constraints/max_parents.py	95.23% <ø> (ø)
motile/constraints/pin.py	96.15% <ø> (ø)
motile/constraints/select_edge_nodes.py	96.00% <ø> (ø)
motile/costs/appear.py	92.85% <ø> (ø)
motile/costs/costs.py	77.77% <ø> (ø)
motile/costs/edge_distance.py	50.00% <0.00%> (ø)
motile/costs/split.py	92.85% <ø> (ø)
motile/costs/weight.py	73.68% <ø> (ø)
motile/ssvm.py	80.95% <ø> (ø)
... and 9 more

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[funkey]

Thanks a lot! :)