Remove an artifact from artifact store as well as
removing value from both database and pickle store if
no other artifacts refer to it.

A KeyError can be raised instead when the pickle file is not found at
the expected location.

There might be a bug with artifact versions so the tests with hardcoded
versions are xfailed.

Allow user to pass in all as a string into the version parameter
of delete to delete all versions of an artifact.

* Fixing pytorch dependencies for integration tests

* Fixing comments for pytorch integration tests

Write is_artifact_version_valid to validate version passed in by user.
Make version a mandatory keyword argument in lineapy.delete API call.
Fix bug in which version was being set to latest when version 0 was
passeed in.
Cast numeric string version to int.

Add version flags to delete calls in tests.