Update LIBCRUNCH environment variables to LIBALLOCS.
Remove commented-out lazy heap typing code, now handled in libcrunch.
heap_index: remove outdated comment and avoid repeated re-initialization attempts.
Tiny fix to comment.
Update heap index to new malloc hooks API. Better encapsulate deep-index layer terminators, and tolerate null alloc_sites.
Move stuff into liballocs.h to avoid performance regressions caused by the split from libcrunch. Tweak visibilities and inlining attributes.