Merge pull request #34 from ip200/feature/readme_tests

- **Scikit-Learn Integration**: Attached `BaseEstimator`, `ClassifierMixin`, and `RegressorMixin` across all primary calibrators to introduce full scikit-learn native compatibility (`Pipeline`, `GridSearchCV`, etc.).

Merge pull request #33 from ip200/feature/readme_tests

updated README.md and added integration tests

updated readme and added tests

Merge pull request #30 from ip200/venn_abers_regression

IVAR example

Update README.md

Update README.md

Merge pull request #29 from ip200/venn_abers_regression

IVAR example

Merge pull request #28 from ip200/venn_abers_regression

IVAR implementation

Merge remote-tracking branch 'origin/venn_abers_regression' into venn_abers_regression

IVAR implementation