Better memory management in Burn Compute

[mepatrick73]

Feature description

Implementing a memory management allocation strategy that is more aggressive in reusing old memory.

• Should reduce memory fragmentation
• Should reduce the memory allocation overhead by reusing unused memory

Feature motivation

Currently the memory allocator just frees unused memory every n allocations. This leads to a very "zig-zaggy" memory usage pattern. Furthermore, if a chunk has some free space, it will not be used by another allocation leading to internal fragmentation.

(Optional) Suggest a Solution

Instead of freeing memory every n allocations, wait until memory usage hits a certain threshold and then try to free unused memory.
Use the idea of offset to reuse free memory within a chunk if there is enough space.