refactor: Make experimental-sliding-sync compile on WASM

[jplatte]

Unfortunately the matrix_sdk::Client is not Send on WASM, which is probably not going to be easy to fix. Since PreviousEventsProvider is never used as a trait object, there should be no harm in relaxing its supertraits (on WASM).

I intentionally left out xtask::ci changes, because I think this should be tested as part of a matrix-sdk-ui WASM check down the line.

Signed-off-by: Jonas Platte jplatte+matrix@posteo.de

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.08%. Comparing base (2ef14de) to head (616fbe9).
Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4474      +/-   ##
==========================================
- Coverage   85.09%   85.08%   -0.01%     
==========================================
  Files         283      283              
  Lines       31778    31778              
==========================================
- Hits        27041    27038       -3     
- Misses       4737     4740       +3     

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[Hywan]

Thanks for the PR!

Closing in favor of #4483 as it contains a commit to remove SlidingSyncRoomInner::client (it's useless, booo dead code, booo).