Pull hashingListSubtract() out of cdi_linux_test.go and into a pkg in util/

[preminger]

Type of issue
Technical debt

Description of issue
In the course of addressing #1394 (PR #1459), we added a utility function hashingListSubtract() in internal/pkg/runtime/launcher/oci/cdi_linux_test.go:253, which subtracts the contents of one array from another, building on capacities in https://github.com/samber/lo/ but capitalizing on the hashability of the array values to do so more efficiently than the prepackaged lo functions do.

This is a fairly general function, though, and so in principle, it doesn't belong buried in the particular unit-test for a particular pkg, and instead should be pulled out to a Singularity-wide location (e.g. under util).

What's currently blocking this, however, is that the function (as well as the lo code it depends on) uses generics, which in turn require Go 1.18 or later, and we're currently holding off on introducing Go 1.18+ dependencies outside of the testing suites.

[dtrudg]

Free to do this now - looking through the major distributions we are focused on (EL / SUSE / Ubuntu, everyone is at least at 1.18 now via a main or community repo package).