feat: /roadmap caching improvements

[SgtPooki]

We have previously resolved some caching issues (i.e. #380), but one remains for /roadmap paths.

The current functionality works as follows:

1. User requests roadmap view
2. /roadmap request is made
3. ServiceWorker has cache and returns it, but request waits until backend responds ("slow loading")

We should speed up responses for this path and also update the fix implemented by #383 is modified so that updated content can be retrieved.

Currently, the fix in #383 does not update the cache for /pendingChild paths unless the root roadmap request is not cached. Some additional optimization and tweaks need to be made here.

Some ideas:

1. SW cache should only ever return immediately (do not keep request open while contacting backend).
   • Updating the cache should happen outside of main req-response workflow. We could use a queue of some sort to track urls returned from SW cache that we need to poll to check for updates, that are sent separately from user request.