fix: improve trap logging

[mafredri]

Thought it'd be nice to improve the trap logging slightly to give more context:

Before:

=== RUN   Test_UnreleasedCalls
=== PAUSE Test_UnreleasedCalls
=== CONT  Test_UnreleasedCalls
    mock.go:442: Mock Clock - Trap Now(..., [])
    mock.go:196: Mock Clock - Now([]) call, matched 1 traps
    mock_test.go:408: trap Closed() with 1 unreleased calls
    mock.go:484: Mock Clock - test cleanup; will no longer log clock events
--- PASS: Test_UnreleasedCalls (0.00s)
PASS
ok      github.com/coder/quartz 0.004s

After:

=== RUN   Test_UnreleasedCalls
=== PAUSE Test_UnreleasedCalls
=== CONT  Test_UnreleasedCalls
    mock.go:442: Mock Clock - Trap Now(..., [])
    mock.go:196: Mock Clock - Now([]) call, matched 1 traps
    mock_test.go:408: trap Now(..., []) Closed() with 1 unreleased calls
    mock_test.go:411: trap Now(..., []) already Closed()
    mock.go:484: Mock Clock - test cleanup; will no longer log clock events
--- PASS: Test_UnreleasedCalls (0.00s)
PASS
ok      github.com/coder/quartz 0.003s

Added a log to select from #24, hence this PR is targeting that one.