feat: otel support

[nirga]

[galkleinman]

I would model it differently. It makes no sense IMO that the request/response and any other nested DTO implements a trait with record_span. There should be a utility object for each request imo, which implements call (which is the actual request handling logic), record_span, end_span, and inside of these functions you do the span attrs assignments. In current impl it looks really weird (at least to me), lines like this:
self.usage.record_span(span); which makes me wonder why should a usage dto "spawn" a new span.

Approving in case you wanna go forward with it, but i would restructure.