wip: migrate from rusqlite to libsql and libsql_sys
Doesn't compile at all yet, we miss thousands of small changes to switch from rusqlite APIs to ours. Still, sqld-libsql-bindings are fully and successfully migrated, so it's a start.
Based on top of https://github.com/libsql/libsql/pull/235
note to myself: the most important thing to remember is that I commented-out support for loading extensions for simplicity, and we definitely need to bring it back, it's a vital part of sqld k, done
one more self note: dump/exporter.rs had some logic based on rusqlite's savepoint API. We don't have it yet, so for now we'd have to handcode it, so that the transaction can roll back to the last savepoint in case of failure.
These changes age badly, so I'll try from scratch, with the libsql crate api being more mature already. There will also be a likely conflict with #694, so I guess it should go first?