Make use of `testing.Short()` to skip long-running tests

We currently have a mechanism to skip various long-running tests by
putting them into a dedicated suite which is skipped if a certain environment
variable is set. We have 2 environment variables - `NO_EXPENSIVE_CRYPTSETUP_TESTS`
and `NO_ARGON2_TESTS`, and the latter makes no sense anyway. We still
test some Argon2 functionality with this set, it just results in tests that take
a long time being skipped.

We should instead convert these suites to just calling `testing.Short()` which
can be set with the `-test.short` commandline argument.

Search the test suites for NO_EXPENSIVE_CRYPTSETUP_TESTS and NO_ARGON2_TESTS, then read how those environment variables currently control long-running tests. Replace that mechanism with testing.Short() and verify the suites are skipped when running with -test.short while the Argon2 functionality tests still run.

Written by the indexing model from the issue text.