Allow copy and paste of commits between worktrees.

### Is your feature request related to a problem? Please describe.

LazyGit allows copying and pasting commits between branches. However, when I try to copy and paste commits between worktrees, then I am unable to.

### Describe the solution you'd like

I would like to copy and paste commits from one worktree to another worktree.

### Describe alternatives you've considered

The only way to currently do it is to delete the worktree so that I can load the two branches within the same worktree. I currently can't load two branches within the same worktree because if an existing worktree already exists for that branch, then I can't load that branch in the current worktree.

### Additional context

N/A

No files or tests are named. Start by tracing LazyGit’s existing commit copy/paste flow and how it handles multiple worktrees, then reproduce the limitation with two worktrees. Done means commits can be copied from one worktree and pasted into another without deleting either worktree.

Written by the indexing model from the issue text.