Tests: Update to version 3 of package:sqlite3

[simolus3]

Update to version 3.x of the sqlite3 Dart package. The package now uses build hooks to load libsqlite3, so we no longer have to:

• download, build and cache specific versions of SQLite in our CI
• add overrides to ensure we don't accidentally use the system's SQLite on macOS

The package would download a precompiled build for the current platform by default, but we can customize it to ensure we'll always have the SQLITE_ENABLE_STMTVTAB compile-time option set. This is used in sync tests to verify that the core extension consistently resets internal prepared statements before returning.

A downside is that we're no longer able to test with older SQLite versions, we can only use a single one without complicating the setup. We could consider downgrading the version we have in crates/sqlite/sqlite if we wanted to test with older versions, but the current setup is probably fine.