This code was an awful hack to provide some semblance of UI
responsiveness while executing DB statements on the main thread.
Instead, we can just run DB statements in a background thread now,
keeping the UI responsive.
We no longer need to worry about pysqlite implicitly beginning
transactions, and can be more explicit about beginning/ending
transactions
save() now also has a trx argument controlling whether a
transaction should be started / left open
Some initial testing with orjson indicates performance varies from
slightly better than pysqlite to about 2x slower depending on the type
of query.
Performance could be improved by building the Python list in rspy
instead of sending back json that needs to be decoded, but it may make
more sense to rewrite the hotspots in Rust instead. More testing is
required in any case.
