feat(base): Make Store::get_rooms wayyy faster

[Hywan]

Store::get_rooms worked as follows: For each room ID, call

• Take the read lock for rooms,
• For each entry in rooms, take the room ID (the key), then call Store::get_room, which…
• Take the read lock for rooms,
• Based on the room ID (the key), read the room (the value) from rooms.

So calling get_rooms calls get_room for each room, which takes the lock every time.

This patch modifies that by fetching the values (the rooms) directly from rooms, without calling get_room.

In my benchmark, it took 1.2ms to read 10'000 rooms. Now it takes 542µs. Performance time has improved by -55.8%.

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• Extracted from feat(base) Client-side sorting, prelude: Implement Client::rooms_stream #3068

[bnjbvr]

Nice! (Would be nice to have a formal benchmark for this, that we can run with cargo-bench, but the change is so obvious and trivial…)

Can you also fix get_rooms_filtered, while you're at it, please? It does something similar.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.82%. Comparing base (868e821) to head (15ab776).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3552      +/-   ##
==========================================
+ Coverage   83.80%   83.82%   +0.01%     
==========================================
  Files         253      253              
  Lines       25854    25890      +36     
==========================================
+ Hits        21668    21703      +35     
- Misses       4186     4187       +1     

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[Hywan]

get_rooms_filtered is updated as part of #3068 (this commit is extracted from #3068) with a filter_map and so on, it's a bit different. Let's focus on get_rooms for the moment.

About the benchmark, I've sadly lost it! Never run git stash clear without being careful… I'll re-add it later with #3068 I believe.

[Hywan]

rooms_filtered is fixed in #3554