Always close backend device before program exit (#258)

If there's a host side crash or exception there is some device cleanup /
shutdown that doesn't automatically happen and will leave the device in
a hung state for the next run.

This change registers an atexit handler so that in most situations a
host side crash will not result in a hung device.

runtime/tools/python/ttrt/common/api.py

@@ -16,6 +16,7 @@
 from pkg_resources import get_distribution
 import sys
 import shutil
+import atexit
 
 from ttrt.common.util import *
 
@@ -171,11 +172,11 @@ def run(args):
 
         system_desc, device_ids = ttrt.runtime.get_current_system_desc()
         device = ttrt.runtime.open_device(device_ids)
+        atexit.register(lambda: ttrt.runtime.close_device(device))
         for loop in range(arg_loops):
             ttrt.runtime.submit(device, fbb, 0, total_inputs[loop], total_outputs[loop])
             print(f"finished loop={loop}")
         print("outputs:\n", torch_outputs)
-        ttrt.runtime.close_device(device)
 
     # save artifacts
     for binary in binaries: