[DEV] Fixing the versions to now start v0.4.dev0

[adam2392]

Begin starting development for v0.4

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[adam2392]

FYI @sampan501 @PSSF23 @YuxinB @SUKI-O @jovo this is the post-release process where we should update the versions in two files and also the doc version switcher.

This is to move our release process to be a bit more decentralized.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f7bb8f6) 88.86% compared to head (b85caa3) 88.86%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #160   +/-   ##
=======================================
  Coverage   88.86%   88.86%           
=======================================
  Files          41       41           
  Lines        3439     3439           
=======================================
  Hits         3056     3056           
  Misses        383      383           

Files	Coverage Δ
sktree/__init__.py	77.77% <100.00%> (ø)

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