jj-lib: refactor jj git clone|fetch to use new GitFetch api directly.
#16792
| Job | Run time |
|---|---|
| 1m 0s | |
| 3m 6s | |
| 3m 16s | |
| 29s | |
| 49s | |
| 40s | |
| 22s | |
| 3m 11s | |
| 2m 34s | |
| 2m 58s | |
| 15s | |
| 16s | |
| 13s | |
| 19m 9s |