Umbra Scanning Bottleneck Possible Mitigations

[apbendi]

Meta issue to document possible mitigations to the bottleneck of announcement scanning:

• [x] Async w/ progress bar (notification when completed)
• [x] Parrallelization
• [ ] Rust based crypto
• [ ] Only scanning blocks after when the user set their stealth keys
• [ ] Caching previously decrypted messages
• [ ] Lazy loading in UI (show detected announcements as they're found rather than waiting for all of them)
• [ ] Sharding the receive table between withdrawn/non-withdrawn
• [ ] Optional server side scanning via viewing key

[mds1]

#377 is another possible mitigation but requires a new contract. We may want a new contract anyway to implement that + NFT support (1, 2)