Add SerializableLock from Dask to use in Config.set

[djhoese]

Closes #17.

This is somewhere between a bug fix and an enhancement. This is a bug fix for a feature that was never advertised 😉. That feature is being able to serialize the Config object. To accomplish this the SerializableLock class has been copied over from Dask.

[codecov]

Codecov Report

Merging #22 (c45f6a6) into main (38a1f7a) will increase coverage by 0.52%.
The diff coverage is 98.82%.

@@            Coverage Diff             @@
##             main      #22      +/-   ##
==========================================
+ Coverage   94.42%   94.94%   +0.52%     
==========================================
  Files           4        6       +2     
  Lines         610      693      +83     
==========================================
+ Hits          576      658      +82     
- Misses         34       35       +1     

Flag	Coverage Δ
unittests	94.94% <98.82%> (+0.52%)	⬆️

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Impacted Files	Coverage Δ
donfig/_lock.py	96.55% <96.55%> (ø)
donfig/config_obj.py	91.05% <100.00%> (ø)
donfig/tests/test_config.py	100.00% <100.00%> (ø)
donfig/tests/test_lock.py	100.00% <100.00%> (ø)

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