Slightly refactor latestEventsUpdater

[S7evinK]

In an attempt to make testing the latestEventsUpdater easier, some moving around of variables and method calls.

[codecov]

Codecov Report

Attention: 37 lines in your changes are missing coverage. Please review.

Comparison is base (8e4dc6b) 65.41% compared to head (9e2afb5) 65.72%.

Files	Patch %	Lines
roomserver/internal/input/input_latest_events.go	53.75%	29 Missing and 8 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3272      +/-   ##
==========================================
+ Coverage   65.41%   65.72%   +0.30%     
==========================================
  Files         509      509              
  Lines       57512    57519       +7     
==========================================
+ Hits        37622    37804     +182     
+ Misses      16001    15881     -120     
+ Partials     3889     3834      -55     

Flag	Coverage Δ
unittests	50.05% <53.75%> (-0.07%)	⬇️

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