test: use kani built-in --harness-timeout option

Set a per-harness timeout of 30 minutes. This should hopefully make it
easier to debug scenarios where proofs end up hanging indefinitely, as
we now no longer hit the pytest timeout, but instead a timeout built
into kani (which should tell us what exact harness timed out).

Signed-off-by: Patrick Roy <roypat@amazon.co.uk>

Author: roypat

tests/integration_tests/test_kani.py

@@ -34,7 +34,7 @@ def test_kani(results_dir):
     # --output-format terse is required by -j
     # -Z unstable-options is needed to enable the other `-Z` flags
     _, stdout, _ = utils.check_output(
-        "cargo kani -Z unstable-options -Z stubbing -Z function-contracts -Z restrict-vtable -j --output-format terse",
+        "cargo kani -Z unstable-options -Z stubbing -Z function-contracts -Z restrict-vtable -j --output-format terse --harness-timeout 40m",
         timeout=TIMEOUT,
     )