Add enough stubs to be able to link CPython build against Limbo's SQLite
compatibility API:
```
export LIBSQLITE3_LIBS=../limbo/target/debug/liblimbo_sqlite3.a
./configure
make -j8
[snip]
gcc -shared Modules/_sqlite/blob.o Modules/_sqlite/connection.o Modules/_sqlite/cursor.o Modules/_sqlite/microprotocols.o Modules/_sqlite/module.o Modules/_sqlite/prepare_protocol.o Modules/_sqlite/row.o Modules/_sqlite/statement.o Modules/_sqlite/util.o ../limbo/target/debug/liblimbo_sqlite3.a -o Modules/_sqlite3.cpython-314-x86_64-linux-gnu.so
thread '<unnamed>' panicked at sqlite3/src/lib.rs:751:5:
not yet implemented
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
fatal runtime error: failed to initiate panic, error 5
make: *** [Makefile:1511: checksharedmods] Aborted (core dumped)
```
All that's left is to actually implement all of this...
This adds initial SQLite C ABI compatibility to Limbo to make sure we
drive the Rust API in the right way that allows us to implement SQLite
semantics.
