## Summary
Fixes#11651.
Fixes#11851.
We were double-closing a notebook document from the index, once in
`textDocument/didClose` and then in the `notebookDocument/didClose`
handler. The second time this happens, taking a snapshot fails.
I've rewritten how we handle snapshots for closing notebooks / notebook
cells so that any failure is simply logged instead of propagating
upwards. This implementation works consistently even if we don't receive
`textDocument/didClose` notifications for each specific cell, since they
get closed (and the diagnostics get cleared) in the notebook document
removal process.
## Test Plan
1. Open an untitled, unsaved notebook with the `Create: New Jupyter
Notebook` command from the VS Code command palette (`Ctrl/Cmd + Shift +
P`)
2. Without saving the document, close it.
3. No error popup should appear.
4. Run the debug command (`Ruff: print debug information`) to confirm
that there are no open documents
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