Allocation Tracking for Rust

[zicklag]

It could be really helpful if Pyroscope allowed me to track allocations as well as CPU cycles for the Rust SDK.

I think integrating it might be relatively simple by configuring a global allocator that could wrap around any other global allocator while tracking allocations and de-allocations.

I'm not familiar with the codebase or the network protocol, though, so I don't know how involved that would be to setup.

It's also worth noting that I could set this up with an opentelemetry metric instead of using Pyroscope to collect the memory allocation info.