Setting `document_ttl` does not lead to any decrease in the database size

[krassowski]

Description

document_ttl does not actually decrease the size of the database.

Reproduce

1. Install ipylab
2. Run jupyter lab --SQLiteYStore.document_ttl=1
3. Create a notebook with one cell:

from ipylab import JupyterFrontEnd
from time import sleep

app = JupyterFrontEnd()

for i in range(1000):
    app.commands.execute('notebook:insert-cell-below')
    sleep(1.1)
    app.commands.execute('notebook:delete-cell')
    sleep(1.1)

4. Observe modifications in the SQLiteYStore around:
   https://github.com/jupyter-server/pycrdt-websocket/blob/3a5648dc937baca71eb9e997a6aaf8e3d6c91654/pycrdt_websocket/ystore.py#L489-L506
5. Notice that squashed_update always increase in size, despite the notebook staying constant

Expected behavior

document_ttl actually influences the document TTL.

Context

pycrdt                    0.12.11
pycrdt-websocket          0.15.4
jupyterlab                4.4.0
jupyter-collaboration     4.0.0

[krassowski]

It looks like stalled #77 could help?

[krassowski]

I don't know how to decode the squashed_update, but this is what I see, with each iteration the length of the thing increases: