microsoft/snmalloc

AI Summary: Implement a mechanism within the snmalloc allocator to accurately track the size of allocated memory on Windows, specifically addressing the limitations of `_msize` and `_recalloc`. This involves leveraging snmalloc's existing custom metadata feature to store a single bit indicating whether an allocation uses the entire allocated space, and if not, storing the unused space in the last byte. This requires careful consideration of the metadata layout and potential interactions with existing snmalloc functionality.