Preliminary data explorer schema / data update and variable delete ev…

…ents, clean up after comm_close kernel messages (posit-dev/positron-python#389)

* Data explorer live update scaffolding

revert changes to test_inspectors.py

Some changes while debugging, need to write unit tests now

Snapshot

Snapshot

Start in on unit tests for variables/data explorer service interactions

sync

Checkpoint, need to find lost code

Some tests for data explorer change events

Fixes to get things working

Fix variables unit test

Looking good here

* Recompute if passing in existing filters/sort keys

* Check that state is preserved through state changes

* code review comments