fix: Reuse write pool for in-memory SQLite

[peasee]

🗣 Description

• Reuses the write connection pool for in-memory SQLite databases

If we spin up a new connection pool, we create a different in-memory database so the read provider isn't reading the same database anymore.

• Updates connection PRAGMA configuration to only execute for file mode SQLite databases

In-memory SQLite databases don't support WAL journal mode, so let's not try to apply it. The other tuning parameters also don't make sense for in-memory databases.