Read Receipts: Allow Timelines to be configured to hide read receipts on state events.

[pixlwave]

This is an mvp attempt at #3065 to fix element-hq/element-x-ios#2338.

The PR adds a new TimelineReadReceiptTracking enum which is used in place of the track_read_receipts boolean to decide whether to enable tracking for all events, just for message-like events or to disable tracking.

When tracking is configured for message-like only, any read receipts on state events are bundled up into the previous event, using the same logic that receipts from filtered events are handled with.

• Public API changes documented in changelogs (optional)

Before	After

[codecov]

Codecov Report

❌ Patch coverage is 99.06542% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 88.66%. Comparing base (73449f4) to head (bd3b58b).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...ix-sdk-ui/src/timeline/controller/read_receipts.rs	94.11%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5900      +/-   ##
==========================================
- Coverage   88.66%   88.66%   -0.01%     
==========================================
  Files         362      362              
  Lines      104399   104447      +48     
  Branches   104399   104447      +48     
==========================================
+ Hits        92569    92606      +37     
- Misses       7499     7509      +10     
- Partials     4331     4332       +1     

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[codspeed-hq]

CodSpeed Performance Report

Merging #5900 will not alter performance

_{Comparing doug/read-receipt-filters (4b903d0) with main (73449f4)}

Summary

✅ 50 untouched