Add version check for sqlite

[simolus3]

When loading the extension, this compares the running SQLite version against the minimum one we expect (3.44.0). When it's older, we abort loading the extension with a descriptive error message:

SQLite version 3.41.0 2023-02-21 18:09:37
Enter ".help" for usage hints.
Connected to a transient in-memory database.
Use ".open FILENAME" to reopen on a persistent database.
sqlite> .load target/debug/libpowersync.dylib
Error: error during initialization: Could not initialize PowerSync: Version 0.4.2 of the PowerSync SQLite extension requires SQLite version number 3044000 or later, but was loaded against 3.41.0 (3041000)

This also expands Dart tests to:

1. Run on macOS as well
2. Test with a recent (3.50.2) and the minimum (3.44.0) SQlite version. I've copied a script from drift to download both of them, and set up a cache to not do that every time.

Finally, I've updated the sqlite version used to build the shell.