--failed-first and --new-first don't play well together

[Gaelan]

When running pytest --new-first --failed-first, I would expect failing and completely new (ie never run before) tests to run first, then the rest of the test suite in order of modification time. Unfortunately, NFPlugin actually seems to sort the entire test list by modification time, clobbering any ordering done by LFPlugin, so --new-first --failed-first is equivalent to --new-first alone.

Running pytest 8.3.2 on Debian bullseye.