tests: use custom allocator in unit tests
tests: use custom allocator in unit tests

This should help make sure that squash_free is only called when memory
is allocated with squash_malloc/realloc (not malloc/realloc).
Additionally, ASan should catch situations when free is called with
memory allocated with squash_malloc/realloc (once we can reenable it,
at least).

Cloudef/squash,quixdb/squash,jibsen/squash,quixdb/squash,quixdb/squash,Cloudef/squash,Cloudef/squash,jibsen/squash,jibsen/squash