&hazrulakmal [ENH] abstract parallelization backend, refactor of evaluate and tuners, extend evaluate and tuners to survival predictors

[fkiraly]

This PR makes the following changes:

• introduces the sktime abstract parallelization backend to skpro. In the future, this should be moved to scikit-base.
• refactors evaluate to use the parallelization backend
• refactors tuners to use the parallelization backend
• extends evaluate to be compatible with survival predictors
• extends tuners to be compatible with survival predictors

Depends on #157 for the survival prediction functionality

Credits @hazrulakmal due to significant parts of copy-paste from sktime evaluate being code written or improved by @hazrulakmal.