Keyboard interrupt: double `Ctrl-C` too quickly hangs the library

[JordanYates]

If a user attempts to terminate the program a second time with ctrl-c, the interrupt handlers deadlock.
Output logs with -v:

I 11:38:54 station_server - Starting station server at:
  Local: http://localhost:4444
  Remote: http://TAURUS:4444
I 11:38:54 test_descriptor - Executing test:
Enter a DUT ID in order to start the test.
^CE 11:38:56 test_descriptor - Received SIGINT, stopping all tests.
E 11:38:56 test_descriptor - Aborting <openhtf.core.test_descriptor.Test object at 0x7f3568580350> due to SIGINT
E 11:38:56 test_descriptor - Test state: <TestState: None@TAURUS Running Phase: trigger_phase>
E 11:38:56 test_executor - Abort test executor.
^CE 11:38:56 test_descriptor - Received SIGINT, stopping all tests.
^CE 11:39:47 test_descriptor - Received SIGINT, stopping all tests.
^CE 11:39:47 test_descriptor - Received SIGINT, stopping all tests.
^CE 11:39:47 test_descriptor - Received SIGINT, stopping all tests.
^CE 11:39:47 test_descriptor - Received SIGINT, stopping all tests

Backtrace from the python debugger:

The nested handler is waiting forever on the test lock, which was already taken by the original handler:

I suspect this would be solved with internal state that checks whether handle_sig_int is already running.

If this does happen, the only way I have found to terminate the program is via the kill command.

openhtf version: v1.6.1
OS: Ubuntu 24.04, under WSL2