Add Codespell to CI, fix typos

[mryab]

This PR applies Codespell to the repo and attempts to fix most of the typos found by this tool; the rest are debatable. Also, it adds Codespell to CI to prevent (or at least highlight) future typos, you can see that it works by navigating the PR diff or the diff for this commit.

[codecov]

Codecov Report

Merging #543 (03cc503) into master (41a2d06) will increase coverage by 0.02%.
The diff coverage is 70.00%.

@@            Coverage Diff             @@
##           master     #543      +/-   ##
==========================================
+ Coverage   75.96%   75.98%   +0.02%     
==========================================
  Files          81       81              
  Lines        7979     7978       -1     
==========================================
+ Hits         6061     6062       +1     
+ Misses       1918     1916       -2     

Impacted Files	Coverage Δ
hivemind/averaging/averager.py	47.85% <ø> (ø)
hivemind/averaging/partition.py	90.65% <ø> (ø)
hivemind/compression/base.py	93.22% <ø> (ø)
hivemind/dht/node.py	90.99% <ø> (ø)
hivemind/dht/routing.py	94.11% <ø> (ø)
hivemind/optim/grad_averager.py	94.11% <ø> (ø)
hivemind/optim/optimizer.py	69.57% <ø> (ø)
hivemind/optim/power_sgd_averager.py	37.07% <ø> (ø)
hivemind/utils/math.py	44.44% <ø> (ø)
hivemind/compression/quantization.py	94.82% <66.66%> (-0.05%)	⬇️
... and 2 more

[mryab]

It might be possible to add ibrary, nd etc. to ignore lists, but we might miss actual typos in this case