feat(ffi): introduce a mark_all_rooms_as_read method for mitigating backend badge count issues

[stefanceriu]

The idea is to introduce a developer option within Element X which would invoke this method and mitigate element-hq/element-x-ios#3151, perhaps help make whatever's wrong on the backend more obvious.
This is a stopgap solution until we can deliver proper app/sdk side unread counting and badge updates.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.91%. Comparing base (777ce05) to head (a5bd0d7).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6550      +/-   ##
==========================================
- Coverage   89.92%   89.91%   -0.01%     
==========================================
  Files         381      381              
  Lines      106860   106860              
  Branches   106860   106860              
==========================================
- Hits        96095    96087       -8     
- Misses       7108     7121      +13     
+ Partials     3657     3652       -5     

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

[codspeed-hq]

Merging this PR will not alter performance

✅ 50 untouched benchmarks

---

_{Comparing stefan/markAllAsRead (a5bd0d7) with main (777ce05)}

[Hywan]

Approving to unblock the situation, but we must not keep this ^^.