[Qrytics]

Running versioningit in a directory that is not under version
control but contains a PKG-INFO file without a Version field crashes
with an unhandled ValueError traceback:

$ versioningit /path/to/sdist
...
ValueError: Metadata does not contain a Version field

Every other user-facing failure in main() is reported as a clean
one-line versioningit: <ErrorType>: <message> on stderr with a nonzero
exit status. A PKG-INFO file without a Version field is just as much
a user/input problem (e.g. a truncated or hand-written file), so it
should be reported the same way.

This change converts the ValueError from parse_version_from_metadata()
into a NotSdistError inside get_version_from_pkg_info(), so the CLI
now prints:

versioningit: NotSdistError: /path/to/sdist contains an invalid PKG-INFO file: Metadata does not contain a Version field

and exits 1 with no traceback. parse_version_from_metadata() itself is
unchanged (it still raises ValueError, as documented and tested), and
the --traceback flag still shows the full traceback when requested.

Test: added test_command_bad_pkg_info to test/test_main.py, which
builds a project dir with a [tool.versioningit] config plus a
Version-less PKG-INFO, runs main(), and asserts exit status 1,
empty stdout, no Traceback on stderr, and a versioningit: NotSdistError: message. The new test fails before the fix (uncaught
ValueError) and passes after; test_main.py, test_get_version.py,
test_util.py, and test_logging.py all pass (199 passed, 1 skipped).