Replace old visible rooms range with subscriptions in the room list.

[pixlwave]

This PR does 2 things:

• Use the visible range publisher once again, this time to add subscriptions to the rooms so we get back the timeline_limit: 20 behaviour.
• Removes the use of roomListItem.unsubscribe() (and tracking the subscription count) as this won't be part of Simplified Sliding Sync.

Closes #3007.

[github-actions]

	Warnings
⚠️	Some of the commits are missing ticket numbers. Please consider squashing all commits that don't have a tracking number.

Generated by 🚫 Danger Swift against 59c18ed

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 19 lines in your changes missing coverage. Please review.

Project coverage is 77.78%. Comparing base (bf9e1d6) to head (59c18ed).

Files	Patch %	Lines
...ervices/Room/RoomSummary/RoomSummaryProvider.swift	0.00%	19 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3014   +/-   ##
========================================
  Coverage    77.78%   77.78%           
========================================
  Files          695      695           
  Lines        53851    53868   +17     
========================================
+ Hits         41886    41901   +15     
- Misses       11965    11967    +2     

Flag	Coverage Δ
unittests	68.60% <0.00%> (+<0.01%)	⬆️

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