wip: tracing/metrics

[kylebarron]

For #105

Well, this is way more complex than I originally thought.

I'm interested in having basic request metrics for an object store: number of requests, their type (get/list/put/delete), timing, and number of bytes downloaded.

At first I was thinking of doing this with a simple Mutex<Vec<RequestStatistics>>, but realized it would lead to horrible lock contention when each request wants to append to the vec.

So I've been looking at the tracing crate and its Instrument, which looks like it might perform better for async code.

However it looks like that's considerably more complex than I want to get into right now.

In theory, a mature implementation of this would allow the Python user to choose where the traces actually go. Like you could set this up to use ObjectStore but send tracing information to, say, CloudWatch

I'll put this stub up just to record my thoughts.

[kylebarron]

Closing in favor of looking at the influxdb implementation: https://github.com/influxdata/influxdb3_core/blob/main/object_store_metrics/src/lib.rs