Add test coverage for the container-based sorter/spiller backend in cases that do not require resumability support (SERVER-120078).

Tests to be parameterized or moved:

• InMemIterTest::SpillDoesNotChangeResultAndUpdateStatistics — parameterize over both FileTraits<> and ContainerTraits<>. Tracker-level assertions (spilledRanges, spilledKeyValuePairs, bytesSpilled*) apply to both backends; file-stats assertions are gated on kHasFileStats.
• FileBasedMakeFromExistingRangesTest::SkipFileCheckingOnEmptyRanges — move to MakeFromExistingRangesTest (already parameterized over both backends). The test passes empty ranges, so no data is read from the resumed spiller; ContainerTraits::makeSpillerForResume needs only a minimal stub returning a fresh spiller.

No changes to production source are required.