[CIS-1087] Fix data races in message list's message count

[dmigach]

My idea was the following:
From the reports on the issue it seemed like the issue is in messages count going out of sync with view's state, so I though of caching message's count and only updating it when we need it

And then I noticed that for channel list there actually already was such a mechanism and it seems like channel list does not experience this kind of issues

The only difference of the suggested fix from the one on the channel list is that message list's structure is a little bit more complicated because it has a VC and a view, but essentially it's the same

[codecov-commenter]

Codecov Report

Merging #1347 (f96b9ad) into main (08b7477) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1347   +/-   ##
=======================================
  Coverage   90.75%   90.75%           
=======================================
  Files         224      224           
  Lines        9800     9800           
=======================================
  Hits         8894     8894           
  Misses        906      906           

Flag	Coverage Δ
llc-tests	90.75% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 08b7477...f96b9ad. Read the comment docs.

[nuno-vieira]

LGTM!

[nuno-vieira]

LGTM