[ENH] dependency and diff test switch for individual estimators to decorate non-suite tests

[fkiraly]

This PR introduces a test switch for individual estimators that can be used to decorate non-suite pytest tests.

The test switch reads the pytest parameters, and if used in a skipif decorator will run the test iff all soft dependencies are present, and if the estimator module has changed (if the ONLY_CHANGED_MODULES switch is on).

This should allow us to minimize test time, by gradually removing all estimator specific costly tests using this decorator.

As a proof of concept, this PR decorates the most costly non-suite tests in the code base (mostly various heavy time series classifier ensembles and such) to be executed only upon module change.

Includes the following changes:

• also checks out main on the test-nosoftdeps-full CI element so it can compute a non-trivial diff to main
• moves the runtime intensive ConformalIntervals doctest into separate pytest tests to allow it to be decorated
• adds missing "numba" dependency tag to the HIVE-COTE classifiers

As both the module of ConformalIntervals and the HIVE-COTE classifiers change (see above), we can consider these test cases, as we would expect the specific non-suite tests for the respective estimators to run in this CI element, while we would not expect the other decorated tests to run.

[yarnabrina]

Added 2 minor non-blocking suggestions, and skipped conformal testing.