tests: do fixed test with random number more times

1000x in this case
tests: add some more list test

nothing big, just test if wl_list_empty() works
tests: add unit tests for wl_signal

Test wl_signal initialization, adding and getting listeners and emitting
tests: extended message when leak in test is detected

When memory or fd leak is detected, print how many blocks of memory were
allocated and not freed, respectively how many files were opened/unclosed.