Add caching to ChangeRequest

[dxinteractive]

Part of the reason for making ChangeRequests is to make Parcels more performant, but hitting the reducer less often. There are two kinds of caching we can add

• Cache calls to ChangeRequest.data() and invalidate the cache after every dispatch step
• Pre-cache data after every dispatch step

[dxinteractive]

Precache after every dispatch step is unnecessary for now, the reducer is more performance that it used to be, and the perf penalty for people not using modifyChange functions is perhaps a little too steep.