…ecessary refactorings to enable downstream functionality (#32)

#### Reference Issues/PRs
This is the most up-to-date PR branch to consolidate all proposed
refactor changes that work with:

- unsupervised trees
- oblique trees
- no performance/runtime regressions against main

#### What does this implement/fix? Explain your changes.
Incorporates refactors to:

Internal Cython of scikit-learn's:
- criterion
- splitter
- tree

Internals of Python in scikit-learns:
- python Tree

Adds the basic implementation of oblique trees. The implementation of
oblique trees has been tested on all sklearn's `check_estimator` testing
function and has error-checking bounds for the new hyperparameter
introduced, which is `feature_combinations` that defaults to ``min(1.5,
n_features)``.

TODO:
1. [ ] ~Add honest support for trees (splitting the data at the Python
API level)~
2. [x] Build wheels
3. [ ] ~Brainstorm unit-tests, or weekly checks to determine when our
fork is out-of-date compared to upstream sklearn~
4. [x] Revamp README for the fork

#### Any other comments?

[cd build]

---------

Signed-off-by: Adam Li <[email protected]>
Co-authored-by: Chester Huynh <[email protected]>
Co-authored-by: Parth Vora <[email protected]>

#### Reference Issues/PRs
Fixes README and wheel building


---------

Signed-off-by: Adam Li <[email protected]>

<!--
Thanks for contributing a pull request! Please ensure you have taken a
look at
the contribution guidelines:
https://github.com/scikit-learn/scikit-learn/blob/main/CONTRIBUTING.md
-->

#### Reference Issues/PRs
<!--
Example: Fixes scikit-learn#1234. See also scikit-learn#3456.
Please use keywords (e.g., Fixes) to create link to the issues or pull
requests
you resolved, so that they will automatically be closed when your pull
request
is merged. See
https://github.com/blog/1506-closing-issues-via-pull-requests
-->


#### What does this implement/fix? Explain your changes.


#### Any other comments?


<!--
Please be aware that we are a loose team of volunteers so patience is
necessary; assistance handling other issues is very welcome. We value
all user contributions, no matter how minor they are. If we are slow to
review, either the pull request needs some benchmarking, tinkering,
convincing, etc. or more likely the reviewers are simply busy. In either
case, we ask for your understanding during the review process.
For more information, see our FAQ on this topic:

http://scikit-learn.org/dev/faq.html#why-is-my-pull-request-not-getting-any-attention.

Thanks for contributing!
-->

---------

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

… fork

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

…urned on (#45)

#### Reference Issues/PRs
Addresses the quantile-trees part of:
neurodata/treeple#29


#### What does this implement/fix? Explain your changes.
1. Stores for each leaf node a 2D numpy array of the y-samples (remember
`y` is (n_samples, n_outputs))
2. Does this all the way in Criterion
3. Only supports supervised tree/splitter/criterion
4. merges in `main` changes.

#### Any other comments?


<!--
Please be aware that we are a loose team of volunteers so patience is
necessary; assistance handling other issues is very welcome. We value
all user contributions, no matter how minor they are. If we are slow to
review, either the pull request needs some benchmarking, tinkering,
convincing, etc. or more likely the reviewers are simply busy. In either
case, we ask for your understanding during the review process.
For more information, see our FAQ on this topic:

http://scikit-learn.org/dev/faq.html#why-is-my-pull-request-not-getting-any-attention.

Thanks for contributing!
-->

---------

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

… into submodulev2

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>

… into submodulev2

Signed-off-by: Adam Li <[email protected]>

Signed-off-by: Adam Li <[email protected]>