Replace dask_ml.wrappers.ParallelPostFit with custom ParallelPostFit class

[sarahyurick]

As part of our initiative to move away from Dask-ML, I've migrated some code from Dask-ML into Dask-SQL to support ParallelPostFit.

[codecov-commenter]

Codecov Report

Merging #832 (ef087db) into main (d9fc2c1) will decrease coverage by 2.10%.
The diff coverage is 30.16%.

@@            Coverage Diff             @@
##             main     #832      +/-   ##
==========================================
- Coverage   77.44%   75.33%   -2.11%     
==========================================
  Files          71       72       +1     
  Lines        3600     3779     +179     
  Branches      634      674      +40     
==========================================
+ Hits         2788     2847      +59     
- Misses        685      795     +110     
- Partials      127      137      +10     

Impacted Files	Coverage Δ
dask_sql/physical/rel/custom/wrappers.py	28.07% <28.07%> (ø)
dask_sql/physical/rel/custom/create_model.py	88.70% <66.66%> (-2.82%)	⬇️
dask_sql/physical/rel/custom/create_experiment.py	96.15% <100.00%> (-0.10%)	⬇️
dask_sql/_version.py	35.31% <0.00%> (+2.74%)	⬆️

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[sarahyurick]

Let me know if you think any tests from Dask-ML's tests/test_parallel_post_fit.py or from dask/dask-ml#912 should be added.

[VibhuJawa]

Remove this documentation link too and your own documentation in dask_sql. I would like us to move away from wrap_fit functionality to auto-detecting if its a sklearn/single-GPU cuML/xgboost model vs a dask model.

[VibhuJawa]

Will be resolved by #855

[VibhuJawa]

Small Change, looks good other-wise

[VibhuJawa]

Requesed Small change, Looks good other-wise.

[VibhuJawa]

LGTM

[ayushdg]

Thanks for this @sarahyurick. Changes generally look good to me.

In addition to some of the integration tests added here which check the interaction of sql with our wrappers, it might make sense (in a followup) to also add unit tests that independently test the wrappers functionality outside of sql and make sure things are working as expected.

We can probably adapt the tests from https://github.com/dask/dask-ml/blob/94e52613fc87abd4ef8c97510539ded1303ae6f4/tests/test_parallel_post_fit.py and add it to the tests/unit section