Tracking Issue: Refactor Service Worker Lifecycle

[TalDerei]

the motivation is detailed in #1573 (tracked in #1376). The necessary work from that issue has been compartmentalized into smaller, distinct work streams. It's a large lift that necessitates extensive testing.

reference the accompanying architectural design document: https://docs.google.com/document/d/1QqP3OfW4Rqa1awYJdTDD9ao8nV8vHDYM4IJjapraHYA/edit

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Phase 1

1. relocate services and block syncing out of the service worker to the offscreen entry #1573

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Phase 2

2. Implement worker scaffolding to enable parallelization  #1787
3. Parallelize the block processor  #1809
4. profile block processor to improve sync performance #1142

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Phase 3

5. improve HandlerContext #924
6. refactor idb database subscriptions to work cross-document #1789

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Potential Low Hanging Fruit

7. minimize storage accesses  #1814