State management: prototype granular stores

[ericpgreen2]

Our current state management package suffers from unnecessary derived store updates, which has numerous downstream performance impacts. It's described in "Problem 1" of https://github.com/rilldata/rill/issues/3960.

Rather than one monolithic store to hold dashboard state, we could split this up into more granular stores. We will prototype this approach for the filters state to assess its performance and ergonomics.