implement support for local extensions (#237)

* implement import_patch

to allow local extensions
closes #172

* implement tests for local_extension

* fix isort

* Revert "implement import_patch"

This reverts commit ed98965f73aa12eb283d317911d62d80eb6b994e.

* implement support for local extensions via AltTemporaryDirectory

as implemented in https://github.com/MichalKubek/cruft/commit/5e3ca7585f9f7c6577e7f6522f32948e8745f74d

* add directory option for AltTemporaryDirectory

* use cruft_state.get to access the directory

for backwards compatibility

* apply isort

* remove unused import

* minor fix for update if repo is there is no directory

* check if name is in sys.path prior to removal

apparently on windows, this might not be the case

* update test repo

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Co-authored-by: Sambhav Kothari <sambhavs.email@gmail.com>