[ENH] Fix failing unit tests

[adam2392]

Fixes #

Changes proposed in this pull request:

• Brings in monotonic constraints to decision trees
• Brings in missing-value support for decision trees and random forests
• Brings up to speed as of 08/16/23 scikit-learn:main

Before submitting

• I've read and followed all steps in the Making a pull request
  section of the CONTRIBUTING docs.
• I've updated or added any relevant docstrings following the syntax described in the
  Writing docstrings section of the CONTRIBUTING docs.
• If this PR fixes a bug, I've added a test that will fail without my fix.
• If this PR adds a new feature, I've added tests that sufficiently cover my new functionality.

After submitting

• All GitHub Actions jobs for my pull request have passed.

[codecov]

Codecov Report

Patch coverage: 97.71% and project coverage change: -0.30% ⚠️

Comparison is base (52bca43) 86.81% compared to head (a647dbe) 86.52%.
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #109      +/-   ##
==========================================
- Coverage   86.81%   86.52%   -0.30%     
==========================================
  Files          24       26       +2     
  Lines        1919     2063     +144     
==========================================
+ Hits         1666     1785     +119     
- Misses        253      278      +25     

Files Changed	Coverage Δ
sktree/ensemble/_supervised_forest.py	100.00% <ø> (ø)
sktree/ensemble/_honest_forest.py	91.46% <61.53%> (-5.68%)	⬇️
sktree/__init__.py	80.00% <100.00%> (+0.83%)	⬆️
sktree/tests/test_honest_forest.py	100.00% <100.00%> (ø)
sktree/tree/_classes.py	74.93% <100.00%> (-1.45%)	⬇️
sktree/tree/_honest_tree.py	100.00% <100.00%> (ø)
sktree/tree/tests/test_all_trees.py	100.00% <100.00%> (ø)
sktree/tree/tests/test_honest_tree.py	100.00% <100.00%> (ø)
sktree/tree/tests/test_tree.py	99.48% <100.00%> (-0.16%)	⬇️
sktree/tree/tests/test_unsupervised_tree.py	100.00% <100.00%> (ø)
... and 1 more

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.