Better handling of compilation memory limit exceeded errors

[prandla]

• check for the sandbox "memory limit exceeded" result in compilation_step.
• change the sandbox so that memory limit is diagnosed more often: specifically, gcc has a driver process which catches the child's death and prints a nice error message. with the previous code this would result in a regular "nonzero return" verdict; now it's memory-limit (though the nice message on stderr is still visible).
• add a new user-visible compilation outcome for it.
• added a test for it. this test tries to use 1.1GB of memory for me, and fails in CMS in around 0.3 seconds, so it should quite reliably trigger the memory limit.
  • currently AWS actually doesn't distinguish the different kinds of compilation failure, so these tests all just assert that some compilation failure happened. this could be made more specific in the future.

[codecov]

Codecov Report

❌ Patch coverage is 42.85714% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.66%. Comparing base (f2af1fb) to head (733f457).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
cms/grading/steps/compilation.py	25.00%	3 Missing ⚠️
cms/grading/Sandbox.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1633      +/-   ##
==========================================
- Coverage   54.66%   54.66%   -0.01%     
==========================================
  Files         335      335              
  Lines       27361    27365       +4     
==========================================
+ Hits        14958    14959       +1     
- Misses      12403    12406       +3     

Flag	Coverage Δ
functionaltests	0.00% <0.00%> (ø)
unittests	54.66% <42.85%> (-0.01%)	⬇️

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[veluca93]

LGTM, but I would want to double check with @gollux :-)