fix(sdk): The LatestEventValue is erased when a room has been emptied

[Hywan]

This patch is twofold:

1. It ensures that a LatestEventValue is erased when a room has been emptied,
2. It implements a test for Ignoring a user doesn't remove their messages from the room list #5317: the LatestEventValue is re-computed when a user is ignored.

Best to review one patch at a time.

---

• Address [meta] Latest Event API, the missing one #4112
• Fix Ignoring a user doesn't remove their messages from the room list #5317

[codspeed-hq]

Merging this PR will not alter performance

✅ 50 untouched benchmarks

---

_{Comparing Hywan:fix-issue-5317 (c739600) with main (92a7d03)}

[codecov]

Codecov Report

❌ Patch coverage is 97.89474% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.93%. Comparing base (92a7d03) to head (c739600).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...trix-sdk/src/latest_events/latest_event/builder.rs	97.89%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6035      +/-   ##
==========================================
- Coverage   88.93%   88.93%   -0.01%     
==========================================
  Files         358      358              
  Lines       99177    99272      +95     
  Branches    99177    99272      +95     
==========================================
+ Hits        88204    88287      +83     
- Misses       6992     7000       +8     
- Partials     3981     3985       +4     

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[poljar]

Makes sense, please just clarify the comment about what's happening bit.