VIT-7076: Buffer, dedup and batch execute background delivery callouts

[andersio]

iOS does not seem to like high CPU usage in background. Syncing multiple resources concurrently seems to be leading to our host app process being frozen.

Change it so that:

1. We now only sync concurrently in foreground.
2. In background, we sync resources serially with batching and prioritisation.
   • Callouts made within a 16ms window are batched up.
   • Within each batch, notified resources are deduplicated, are sorted by their priority, and are then scheduled for execution serially.

[linear]

VIT-7076 Prioritize resource syncs in background

[andersio]

• VIT-7076: Buffer, dedup and batch execute background delivery callouts #226 👈
• VIT-7076: Refactor how resource priority is modelled #225
• main

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[andersio]

Merge activity

• Aug 2, 6:15 AM EDT: @andersio started a stack merge that includes this pull request via Graphite.
• Aug 2, 6:18 AM EDT: Graphite rebased this pull request as part of a merge.
• Aug 2, 6:19 AM EDT: @andersio merged this pull request with Graphite.