Need for support for purely observable self-updating state

## Describe the task

We continue running into the case of needing in state objects which are self-updating. Having these by the existing Feature paradigm means that they are effectively invalid on tick.

Examples:

- Player input snapshot; having one source of truth that can be accessed as state for current player input is highly useful, but as Feature would require dispatch/invalidation per frame
- Timers being held in state; countdowns and the like are useful to keep in state for cross-system synchronisation, but again would either require per-frame dispatch or per-frame invalidation of state

## Completed When

- [ ] A method of handling such cases is developed.