[ENH] survival prediction compositor - reducers to tabular probabilistic regression

[fkiraly]

This PR adds two survival prediction compositors which take probabilistic supervised regressor (including possibly a survival capable regressor) and create survival predictors - i.e., reducers from survival prediction to probabilistic supervised regression.

The two compositors added are common simple baselines in survival regression:

• FitUncensored - subsets to uncensored data and fits on the subsample
• ConditionUncensored - adds C as column in fit, and fills 0 (uncensored) for the same column in predict-like methods.

Depends on #157

[codecov]

Codecov Report

Attention: 116 lines in your changes are missing coverage. Please review.

Comparison is base (86cc53b) 64.82% compared to head (949b743) 63.93%.

❗ Current head 949b743 differs from pull request most recent head 84d612d. Consider uploading reports for the commit 84d612d to get more accurate results

Files	Patch %	Lines
skpro/survival/coxph.py	20.40%	39 Missing ⚠️
skpro/survival/compose/_reduce_cond_unc.py	31.81%	30 Missing ⚠️
skpro/regression/base/_base.py	48.97%	17 Missing and 8 partials ⚠️
skpro/survival/compose/_reduce_uncensored.py	40.90%	13 Missing ⚠️
skpro/regression/compose/_pipeline.py	27.27%	8 Missing ⚠️
skpro/regression/base/_delegate.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #161      +/-   ##
==========================================
- Coverage   64.82%   63.93%   -0.89%     
==========================================
  Files         110      114       +4     
  Lines        5705     5870     +165     
  Branches     1069     1087      +18     
==========================================
+ Hits         3698     3753      +55     
- Misses       1722     1825     +103     
- Partials      285      292       +7     

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