Fix GitArchivePackager when repo or output paths contain spaces - #645

Summary

GitArchivePackager fails when the repository path, job directory or archive name contains spaces. A few shell commands still interpolate these paths without quoting them.

This change uses shlex.quote for Git path discovery and the final gzip/cleanup commands, following the quoting already used elsewhere in the packager. It also expands ~ explicitly so home-relative repository paths continue to work after quoting.

Repository paths are now treated literally rather than as shell expressions; expand environment variables such as $HOME before passing them in basepath.

Archive contents and packaging options are unchanged. This is separate from #637, which fixed PatternPackager; it does not change include-pattern, subpath or submodule handling.

Testing

• Added six cases using a real Git repository and real git/tar/gzip commands: ordinary paths, a repository path with spaces, the basepath override, output directories and archive names with spaces, and a home-relative basepath.
• The original four space-path cases fail before the fix; the ordinary-path control passes. All six cases now pass and check archive contents and removal of temporary files.
• Packaging suite: 30 passed.
• Full suite with the repository's locked dependencies on Linux/Python 3.11: 1,700 passed, 1 deselected, 1 xfailed. Run in a fresh /tmp mount because existing unrelated /tmp/exp1 state on the host breaks eight NVCRE tests on both main and this branch. The original host file was left untouched.
• Ruff check/format and git diff --check passed.

The full run exits successfully; the installed Ray package still emits a non-failing missing-ray.dag message during interpreter shutdown.