move git into common/git.py old-commit-hash: 4fbc8a389662f82018eeabd03294cc761b87ce75
* flags * update ref * use the flags directly * use post_init (don't freeze) * we can maintain frozen with custom class * not preglobal * move to common * cleanup old-commit-hash: 3a6c3315ab181bf7390ae1faa6e87c93b1a97338