Ruby's MEMMOVE takes in the element data type for the third argument, not
the size of the element. What this did was do sizeof(sizeof( ... )) which
always returned sizeof(size_t).

darray.h no longer depends on internal/bits.h, so we can remove it.

We can wrap in DURING_GC_COULD_MALLOC_REGION instead.

assert does not print the bug report, only the file and line number of
the assertion that failed. RUBY_ASSERT prints the full bug report, which
makes it much easier to debug.

[Feature #19783]

This commit adds support for weak references in the GC through the
function `rb_gc_mark_weak`. Unlike strong references, weak references
does not mark the object, but rather lets the GC know that an object
refers to another one. If the child object is freed, the pointer from
the parent object is overwritten with `Qundef`.

Co-Authored-By: Jean Boussier <byroot@ruby-lang.org>

These functions manipulate darray without the possibility of triggering
GC, which is used for places that cannot trigger GC. These functions
crash when the allocation fails.