feat: use shallow clones for backups

[amolenaar]

Checkout only the latest commit for a branch, just enough to create a new commit upon.

Fixes #209.

[amolenaar]

Here's the output of some more thorough testing of the backup process.

Preparation

Created a bare repository:

git init --bare myrepo

First backup on fresh branch

[master (root-commit) 2369e91] Backup
 6 files changed, 833 insertions(+)
 create mode 100644 .project
 create mode 100644 CommitHistory.activitymetadata
 create mode 100644 CommitHistory.json
 create mode 100644 Test.afm
 create mode 100644 Test.aird
 create mode 100644 Test.capella
Enumerating objects: 8, done.
Counting objects: 100% (8/8), done.
Delta compression using up to 8 threads
Compressing objects: 100% (8/8), done.
Writing objects: 100% (8/8), 9.04 KiB | 9.04 MiB/s, done.
Total 8 (delta 1), reused 0 (delta 0), pack-reused 0
To /tmp/myrepo
 * [new branch]      HEAD -> my-branch
INFO:Importer:Backup of model finished

Second backup on existin gbranch

[my-branch 4d5ab1f] Backup
 2 files changed, 176 insertions(+), 176 deletions(-)
Enumerating objects: 7, done.
Counting objects: 100% (7/7), done.
Delta compression using up to 8 threads
Compressing objects: 100% (4/4), done.
Writing objects: 100% (4/4), 721 bytes | 721.00 KiB/s, done.
Total 4 (delta 3), reused 0 (delta 0), pack-reused 0
To /tmp/myrepo
   2369e91..4d5ab1f  HEAD -> my-branch
INFO:Importer:Backup of model finished

Check the repo

root@fedora:~# git clone --branch=my-branch /tmp/myrepo
Cloning into 'myrepo'...
done.
root@fedora:~# cd myrepo/
root@fedora:~/myrepo# ls
CommitHistory.activitymetadata  CommitHistory.json  Test.afm  Test.aird  Test.capella
root@fedora:~/myrepo# git log
commit 4d5ab1fb9bc865d957ef853bc68d2c2775d06ffd (HEAD -> my-branch, origin/my-branch)
Author: user <[email protected]>
Date:   Fri Oct 13 16:41:39 2023 +0000

    Backup

commit 2369e91ccfd5c388fa12c35c0d998c85ede0ea8f
Author: user <[email protected]>
Date:   Fri Oct 13 16:39:02 2023 +0000

    Backup

root@fedora:~/myrepo#

[MoritzWeber0]

Nice improvement and thanks for testing it 🥳