fix(sdk): new_local returns an Option

[Hywan]

Based on top of #5968. Must be merged before.

We can't use LatestEventValue::None as an optional value anymore, since it erases the previous LatestEventValue. This patch update LatestEventValueBuilder::new_local to return an Option to handle all the cases where a local value cannot be computed.

---

• Fix Sending a reaction temporarily bumps a room to the *bottom* of the list. #5958
• Address [meta] Latest Event API, the missing one #4112

[codspeed-hq]

CodSpeed Performance Report

Merging #5969 will not alter performance

_{Comparing Hywan:fix-issue-5958 (059bcd2) with main (4e90cea)}

Summary

✅ 50 untouched

[codecov]

Codecov Report

❌ Patch coverage is 91.04478% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.51%. Comparing base (4e90cea) to head (059bcd2).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...rates/matrix-sdk/src/latest_events/latest_event.rs	90.62%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5969   +/-   ##
=======================================
  Coverage   88.51%   88.51%           
=======================================
  Files         363      363           
  Lines      103590   103638   +48     
  Branches   103590   103638   +48     
=======================================
+ Hits        91688    91738   +50     
+ Misses       7538     7534    -4     
- Partials     4364     4366    +2     

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[jmartinesp]

Thanks!