Consider setting an rlimit for the test suite

[parno]

If the user does not specify an rlimit via the VERIFY_EXTRA_ARGS environment variable, then the args we pass to the verifier are instantiated via a default() call:
https://github.com/secure-foundations/verus/blob/b44a565193338c90fa50fe2f0620664cf6f26d0f/source/rust_verify/tests/common/mod.rs#L124
This appears to set the rlimit to 0, which means a test can potentially run forever. I might suggest that we add something like:

         our_args.verify_pervasive |= verify_pervasive;
+        our_args.rlimit = DEFAULT_RLIMIT_SECS;
         our_args

I tried this as an experiment, and on the CI machine, it causes e18_pass from rust_verify/tests/summer_school.rs to fail, so we may want to tweak that test or introduce the ability to locally increase the rlimit before adopting a test-suite-wide rlimit.

[parno]

We discussed this in today's Verus meeting and the consensus seemed to favor this change. I might wait to attempt it until after the interpreter branch is merged, since that would be one deterministic way to fix the e18_pass test.

[utaal]

The test suite now uses Verus' global default (--rlimit 10), as we are just calling the regular verus binary for tests (instead of instantiating a verifier in-process).