test: use stronger assertions in util tests

[nogeenhenk]

Summary

Address AI findings in tests/auto/util/tst_util.cpp:

• Use exact counts (>= 3, == 1, >= 2) instead of weak assertions (>= 2, > 0, >= 1)
• Use QCOMPARE instead of QVERIFY for equality checks in namedValuesEdgeCases for better test failure messages

[coveralls]

coverage: 18.572%. remained the same
when pulling 94d9be7 on fix/test-assertions
into 790ca75 on main.