gdb: Ctrl-C then continue cancels the guest call #1973

After gdb interrupts a running guest, continue or detach makes the guest call fail with ExecutionCanceledByHost.

The Cancelled arm handles the debug stop, then always falls through to break Err(RunVmError::ExecutionCancelledByHost) (hyperlight_vm/mod.rs#L769). kill_from_debugger sets only the debug bit, so the cancel was never requested. The behavior dates back to #924.

Repro: attach gdb to a sandbox calling SpinForMs(15000), interrupt, then detach. The call returns ExecutionCanceledByHost. Confirmed with a gdb example test.

Fix: after handle_debug(Interrupt) returns, continue the run loop unless cancel_requested is set.