Statement.cancel() causes lockup

[mrotteveel]

See also https://groups.google.com/g/firebird-java/c/WDsY8fBLmyo/m/r56MBQefAAAJ; it looks like cancelling a statement too quickly after execution might have some race condition or incorrectly registers or doesn't unregister a deferred operation, causing a subsequent hang of the connection waiting for data.

There currently is no clear reproduction recipe.

If a fix is found, it will probably need to be backported to Jaybird 5 as well.

[mrotteveel]

Issue #903 will overhaul locking for Jaybird 7 to fully address the thread-safety issue; for Jaybird 5 and/or 6 we'll create a reduced solution (probably only covering FbWireStatement implementations).

Fixing the thread-safety will not necessarily address all problems with cancellation, so it may need additional investigation after those changes.

[mrotteveel]

See also jdp-2026-02: Cancellation thread-safety backport