Saving modified Items only when they are dirty

[jtle00]

The original proposal can be seen in issue #9, bullet point 2.

2. "Use something like updateZarr() to save modified items (e.g. dirty items) during runtime. Idea here is that during normal editing runtime, we have some granuality on which part of zarr to save. If points have been edited then save them. Only save parts that are dirty."

Hi @Suhayb-A, amazing work on the Core! Is there currently a way to check if the points and lines data frame have been modified/ dirty so we that can update them individually?

[cudmore]

This is also important to decide if we need to save a mmap on quit. When user quits, we need to save if the mmap is dirty.