Add rememberEventSink

[stagg]

Helper to control stability of extracted event sinks.

[chrisbanes]

To me, this looks like more of a signal that we should separate out the CircuitState and events. Bundling in the event sink into the state makes implementation simpler, but we're conflating two different things here (which is why stability is an issue).

[ZacSweers]

Talked a little offline

• @stagg is gonna write some tests to test some assumptions. We've heard downstream that compose-compiler automatically remembers lambdas in some (most? all? who knows!) cases that may make this redundant, but we've seen inconsistent behavior
• Discussed a bunch with Adam and Bill separately and put up some prototypes of alternative state designs in Prototype different state designs #1077 if you wanna peek

[stagg]

Going to verify this in a separate test PR.