For interactive programs, we do not set time limits correctly

[gkreitz]

While fixing up things flagged by ruff check, I noticed that val_timelim when running a validator for an interactive problem was an unused variable. From a quick glance, I'm not sure if the submission gets correctly time limited either, it seems like we may only set a wall time limit of 2*timelim (but I haven't dug deeper, in case there is some subtle path setting timelim for the submission).

Somewhat related to #166 (which shows traces of interactive previously having set a time limit).

[gkreitz]

The end result ended up being almost correct here, but there are corner case bugs stemming from this. validate_interactive will currently only return TLE for submissions that run longer than 2 * timelim in walltime. This is clearly incorrect. The reason is that interactive long ago used to ulimit cpu time, but no longer does (but the python code was not updated to handle this).

The bug was mostly hidden by the fact that run_submission_real (which looks at how sensitive a submission is to if the time limit is lower or higher) would notice that the runtime is above timelim, and adjust the results. This has the consequence that we continue to run test cases, and we can get weird warnings. For instance, here is a run where I've rigged a solution to use 3 seconds of CPU time (well above the time limit of 1, but below the wall time limit which ends up being 4s here):

WARNING TLE submission guess_tle_with_alarm.cc (C++) sensitive to time limit: limit of 1 secs -> TLE, limit of 2 secs -> AC
   TLE submission guess_tle_with_alarm.cc (C++) OK: TLE [testcase: testcase secret/03, CPU: 3.00s @ testcase secret/03]

Note that the warning is just completely incorrect, the submission runs for 3 seconds, so a time limit of both 1 and 2 seconds would have made it a TLE.

I'm not sure if there's additional impact for multipass. I don't think there is, but I haven't dug through the code more. Instead, I'll just fix interactive to look at the timelimit and return TLE if more time is used. Adding an ulimit would be nice (it would make it time out faster), but I'll leave that for a future interactive rewrite.