Cleanup fastbin_dup_consolidate and prepare it for glibc version 2.41

[k4lizen]

Handles: #200

Clarified some language to make it more clear this isn't a technique that (in general) gives tcache double free -> tcache poison. Cleaned up the explanation a bit.

I didn't touch versions 2.24 and 2.23 (which don't have tcache).

[Kyle-Kyle]

Hi, the change looks good. But it seems there are some extra comments related to tcache-poisoning in the file, such as

// We would have to allocate this to be able to do tcache poison later, since we need at least 2 chunks in a bin to do it.
// void* ppoison = malloc(CHUNK_SIZE);

Since tcache-poisoning is another technique, and it is kinda confusing to explain another technique in another one. Can you please remove them before I hit merge?

[k4lizen]

Alright

[k4lizen]

@Kyle-Kyle no rush but just a reminder in case you forgot