fix: resolve dune build @check warnings and errors
memtrace/bin: fix unused warnings (remove unused type timestamp,
unused val length, prefix unused field _added_before, prefix unused
val _avg_dist_to_alloc) instead of suppressing with -w flags.
xdge/test: consolidate into single test runner, remove .mli files
that triggered dune @check bug (Alcotest unbound in bytecode check),
merge test_paths suite into main test executable.