Change rlimit nproc resource limit to apply to the autotester process

[ch-iv]

This PR changes the resource limit on the number of extant processes (resource.RLIMIT_NPROC) to apply to each individual worker rather than to the entire docker user.

Refactors the set_rlimits_before_test function to remove the nproc adjustment, because it became obsolete due to earlier changes.

Adds a small change to how the rlimit value is validated. Previously the soft limit would be set to min(soft, hard), however that produced an incorrect result when hard = resource.RLIMIT_INFINITY (-1).

Adds tests for get_resource_settings, get_setrlimit_lines, and validate_rlimit.

[ch-iv]

@david-yz-liu Requesting review.

[david-yz-liu]

@ch-iv great work. I left a few inline comments; also please update the changelog.

[david-yz-liu]

Please omit the initializer entirely (as it isn't doing anything other than forwarding the arguments)

[ch-iv]

Could you please clarify how you want me to do this, because I've tried a few things, but none of them worked.

I've tried:

class MockTester(Tester):
    def run(self) -> None:
        pass

In the above code I get TypeError: Can't instantiate abstract class MockTester without an implementation for abstract method '__init__'.

I've also tried:

class MockTester(Tester):
    def __init__(
        self,
        specs: TestSpecs,
        test_class: Type[Test] | None = Test,
        resource_settings: list[tuple[int, tuple[int, int]]] | None = None,
    ) -> None:
        pass

    def run(self) -> None:
        pass

Which raises AttributeError: 'MockTester' object has no attribute 'resource_settings'.

Then I asked chat, which suggested to do:

class MockTester(Tester):
    __init__ = Tester.__init__

    def run(self) -> None:
        pass

But I still get TypeError: Can't instantiate abstract class MockTester without an implementation for abstract method '__init__'

I think this is because the Tester.__init__ method is defined as abstract, so it has to be implemented in the MockTester class. However, Tester.__init__ also does some setup, so all classes inhering from Tester must either call Tester.__init__ or reimplement that setup logic.

[david-yz-liu]

@ch-iv you're right about this, I had missed the @abstractmethod decorator on the initializer. I'm good to leave this as-is!

[david-yz-liu]

Nice work, @ch-iv!

[david-yz-liu]

@ch-iv you're right about this, I had missed the @abstractmethod decorator on the initializer. I'm good to leave this as-is!