feat(base): Remember the inviter if we accept an invite

[poljar]

Another PR that is a prerequisite of #5322.

Par of #4926.

• Public API changes documented in changelogs (optional)

[codecov]

Codecov Report

Attention: Patch coverage is 93.10345% with 4 lines in your changes missing coverage. Please review.

Project coverage is 88.78%. Comparing base (edd371b) to head (d38285b).
Report is 2 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/matrix-sdk-base/src/room/room_info.rs	70.00%	3 Missing ⚠️
crates/matrix-sdk/src/client/mod.rs	88.88%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5390   +/-   ##
=======================================
  Coverage   88.78%   88.78%           
=======================================
  Files         334      334           
  Lines       91280    91317   +37     
  Branches    91280    91317   +37     
=======================================
+ Hits        81040    81078   +38     
+ Misses       6410     6409    -1     
  Partials     3830     3830           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[Hywan]

Approving, thanks for the work. I'm leaving one question, not a blocker.