[backport] bump functors compat

[ericphanson]

Backport of #27

• I created a release-0.1 branch from e3fd92e
• I added branch protection to it
• Then on this branch I repeated the exact same steps as in bump functors compat #27 (update Functors 0.4, verify current tests pass, update model to have weight sharing, write it out on Fucntors 0.3, test it on Functors 0.4)

[codecov]

Codecov Report

Merging #28 (516958c) into release-0.1 (e3fd92e) will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           release-0.1      #28   +/-   ##
============================================
  Coverage        93.87%   93.87%           
============================================
  Files                2        2           
  Lines               49       49           
============================================
  Hits                46       46           
  Misses               3        3           

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[kleinschmidt]

reminds me I shoudl turn on branch protection for my other backport branches 👀