Experiment with a custom Kysely SQLite dialect

[goto-bus-stop]

June 2025 update: This is probably not necessary for now. Synchronous SQLite with good indexes shouldn't really be an issue for a typical small-scale server. It's not great that it blocks the main thread, but it's not the most urgent problem either.

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In particular:

• Support async transactions
• Connection pooling (async transactions requires using other connections for other requests)
• Reusing most recent prepared statement especially for repeated inserts

This has one big downside for the tests: connection pooling prevents using a named in-memory store with better-sqlite3.

To explore:

• Can we use libsql like this? AFAICT the official libsql dialect for kysely is outdated and has serious bugs.
• Execute queries on worker threads to allow JS to run while queries are in progress.