USDTs on important functions

Other popular allocators, such as jemalloc have built-in mechanisms for profiling; mimalloc does not. To allow some level of debugging, it would be great if mimalloc added [USDTs](https://www.oreilly.com/library/view/linux-observability-with/9781492050193/ch04.html#:~:text=user%2Dspace%20programs.-,User%20Statically%20Defined%20Tracepoints,tracing%20capabilities%20that%20BPF%20offers.) in important places, such as at the end of `malloc` and `free`. USDTs have a very minimal impact when not being traced (inserts a single NOP instruction) and much lower impact than having to use uprobes/uretprobes.

Is this something that would be accepted into the mimalloc project?

Start by reviewing the allocator entry points named in the issue, especially malloc and free, along with the linked USDT background. Determine which important functions and tracepoint behavior the project would accept, then verify that tracing works and that the untraced path retains the stated minimal overhead.

Written by the indexing model from the issue text.