Rename all CBMC proof allocators

Most of the allocator have the prefix `ensures` something is allocated. This is not precise, because this allocators **non-deterministically** allocate memory, so at the end there could be null pointers. Rename them to reflect their behavior.

Search the repository for CBMC proof allocators whose names use the `ensures` prefix and inspect every reference to them. Rename the allocators and their references to describe non-deterministic allocation, then run the repository's available checks to confirm the proof code still builds and all names are consistent.

Written by the indexing model from the issue text.