test: add failing test reproducing #113 (GIL held during blocking I/O) - #114

…ing I/O)

cursor.execute() (and commit/rollback/fetch*/executemany/
executescript) call into blocking Rust code without releasing the
GIL. When the underlying call blocks -- e.g. waiting on sqlite's busy
handler for a lock, or (per the linked issue) on a stuck Hrana stream
-- the whole interpreter freezes, including any other Python thread.
This is why a concurrent.futures-based timeout wrapped around the
call from another thread never fires: the watcher thread's timed wait
elapses at the OS level, but it then blocks trying to reacquire the
GIL from the thread stuck inside the extension call, since that
thread never released it.

This test blocks one connection against another via sqlite's busy
handler (no remote server required) and asserts a background thread
keeps ticking during the wait. It currently fails:

    AssertionError: background thread only ticked 2 times while
    cursor.execute() was blocked for ~1.5s -- GIL was likely held
    during the blocking call

Ref: tursodatabase#113