fix: prevent snapshot from tracking large files

[goniz]

This PR prevents the Snapshot.track() flow from adding (untracked) big files into the snapshot system (git).

It changes the code to first do git add -N . which stage the files without content.
Next it iterates over the staged files to find any files larger then defined threshold (1 gig). unstages them AND adds them to $gitdir/info/exclude to prevent them from getting staged again.
Finally it calls git add -- $stagedFiles to stage the files content as well.

To handle existing bloated snapshot dirs, the cleanup method was updated to detect if any existing object blob is bigger then threshold -> nukes the whole snapshot dir.
Leaving the big files causes the git gc --prune process to blow up on memory and hog the system.

Additionally, this PR cleans up the Snapshot code a bit.

Don't be scared from the lines added, I've added tests too 😆

Fixes #6845

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on the search results, I found one potentially related PR:

Related PR:

• PR feat: bugfix to snapshot pruning and allow snapshot config to accept positive integer for retention lifespan in days (resolves #10626, #10782, #6845, #3182, #10532) #10628 - "feat: bugfix to snapshot pruning and allow snapshot config to accept positive integer for retention lifespan in days (resolves [FEATURE]: Snapshot lifespan ought be configurable. #10626, Old snapshot folders not deleted after the 7 day threshhold #10782, HUGE snapshot folder #6845, Very slow session due to 98GB of git snapshots #3182, Opencode using my 20 GB storage #10532)"
  • feat: bugfix to snapshot pruning and allow snapshot config to accept positive integer for retention lifespan in days (resolves #10626, #10782, #6845, #3182, #10532) #10628
  • This PR also addresses issue HUGE snapshot folder #6845 (the same issue referenced in PR fix: prevent snapshot from tracking large files #12185), and it's related to snapshot management and cleanup. It may be addressing the same underlying problem or be a related approach to handling snapshot files.

You should verify if PR #10628 has already been merged or if it addresses the same root cause as PR #12185.

[goniz]

Self review 😄