Spaces: Add a method to reset a SpaceRoomList.

[pixlwave]

We now have the ability to add/remove space children in #5871, however as the SpaceRoomList is based on /hierarchy it isn't aware of any changes made by the space service. This PR helps by making a way to reset the list so that the next paginate() call starts from the beginning again.

Whilst we could listen for m.space.child/parent events in the sync loop, this wouldn't help if you removed a room where you aren't a member.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.94%. Comparing base (0053ecb) to head (06744f9).
⚠️ Report is 21 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6043   +/-   ##
=======================================
  Coverage   88.94%   88.94%           
=======================================
  Files         358      358           
  Lines       99283    99312   +29     
  Branches    99283    99312   +29     
=======================================
+ Hits        88308    88337   +29     
+ Misses       6988     6987    -1     
- Partials     3987     3988    +1     

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[codspeed-hq]

Merging this PR will not alter performance

✅ 50 untouched benchmarks

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_{Comparing doug/reset-space-list (06744f9) with main (0053ecb)}

[stefanceriu]

Beautiful, looks good to me 👍