e2e: nothing catches actor metric continuity across suspend/resume

#761 reported that an actor's own counters merge and inflate across a suspend/resume, silently.
Everything in `internal/e2e` is platform plane, where we own the emitter, and we don't have coverage for workload emitted telemetry today.

So I'd like a small test where an actor increments a counter, we suspend and resume it, and we assert the total afterwards is a sum of what the actor actually counted rather than a reset artifact.

It would be nice to have this while we are designing #853 as

* behaviour-wise this is what we want, regardless of the final relay design
* it can help validating our relay design

Note: this will fail today, but that's the point. We probably want to mark it as optional until the relay lands, what do you all think?

High level idea:

* a tiny actor that counts something and exports otlp. The demo in #750 may already give us this, and I'd rather not build a second one
* assert on the delta across the lifecycle operation, not on an absolute value

cc @git286 @JeffLuoo @sanskar-singh-2403 @maxsmythe