fix(sdk): Latest Event lazy-loads the Room Event Cache

[Hywan]

This patch improves Latest Events in multiple ways.

First off, the system is lazier. Before, a LatestEventValue was initialized by computing a Remote(_) with the help of the RoomEventCache. Now, it is initialized by copying the value in the RoomInfo. It solves a bug where a latest event was registered but its corresponding RoomEventCache was not created yet.

Second, in addition to that, if the restored LatestEventValue is None, a lazy computation is asked from the Event Cache. It fixes a bug where the RoomInfo has no LatestEventValue but it's possible to compute one from the Event Cache.

Finally, replacing a LatestEventValue::None by itself is ignored, thus reducing the number of updates in the system.

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• Address [meta] Latest Event API, the missing one #4112

[codspeed-hq]

CodSpeed Performance Report

Merging #5947 will improve performances by ×5

_{Comparing Hywan:fix-sdk-latest-event-lazy-load-room-event-cache (351c604) with main (ce65317)}

Summary

⚡ 1 improvement
✅ 49 untouched

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	Create[1000 rooms × 1000 events]	30.7 ms	6.1 ms	×5

[codecov]

Codecov Report

❌ Patch coverage is 95.14066% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.50%. Comparing base (f2ba338) to head (351c604).
⚠️ Report is 10 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...matrix-sdk/src/latest_events/room_latest_events.rs	77.08%	8 Missing and 3 partials ⚠️
crates/matrix-sdk/src/latest_events/mod.rs	96.38%	2 Missing and 4 partials ⚠️
...rates/matrix-sdk/src/latest_events/latest_event.rs	98.85%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5947      +/-   ##
==========================================
- Coverage   88.50%   88.50%   -0.01%     
==========================================
  Files         362      362              
  Lines      103395   103405      +10     
  Branches   103395   103405      +10     
==========================================
+ Hits        91512    91520       +8     
+ Misses       7533     7529       -4     
- Partials     4350     4356       +6     

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[jmartinesp]

I can approve this from the client side perspective, but someone else should probably take a deeper look at the code.