Document repo analytics

[cgarciae]

What does this PR do?

Documents how to run the repo analytics and does some cleanup.

[cgarciae]

Thanks @gnecula for reviewing it. Updated the script to use absl.

[codecov-commenter]

Codecov Report

Merging #2317 (37fea7b) into main (e7742de) will decrease coverage by 0.87%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #2317      +/-   ##
==========================================
- Coverage   75.83%   74.95%   -0.88%     
==========================================
  Files          61       62       +1     
  Lines        5383     5491     +108     
==========================================
+ Hits         4082     4116      +34     
- Misses       1301     1375      +74     

Impacted Files	Coverage Δ
flax/jax_utils.py	42.85% <0.00%> (-23.81%)	⬇️
flax/training/checkpoints.py	81.70% <0.00%> (-15.25%)	⬇️
flax/serialization.py	66.06% <0.00%> (-1.82%)	⬇️
flax/errors.py	88.75% <0.00%> (-1.80%)	⬇️
flax/ids.py	96.00% <0.00%> (ø)
flax/linen/module.py	93.79% <0.00%> (+0.02%)	⬆️
flax/core/scope.py	89.93% <0.00%> (+0.04%)	⬆️
flax/linen/transforms.py	89.76% <0.00%> (+0.08%)	⬆️

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