feat: store the thread subscription status in the database

[bnjbvr]

Some implementation notes:

• instead of using kvdata (StateStoreDataKey et al.), I've added a new table for the thread subscriptions, so we can later do queries like "where status is subscribed".
• I've made it so that unsubscribing is remembered on the local device, so the next attempt to fetch a thread subscription may return unsubscribed. The MSC should soon evolve in that direction, in such a way that a thread status can be unsubscribed on the server as well, so I'm just being a bit early here.

[codspeed-hq]

CodSpeed Performance Report

Merging #5455 will not alter performance

_{Comparing bnjbvr/store-thread-subs (d2d9b9c) with main (8091094)}

Summary

✅ 6 untouched benchmarks

[codecov]

Codecov Report

❌ Patch coverage is 90.13158% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.90%. Comparing base (8091094) to head (d2d9b9c).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/matrix-sdk-sqlite/src/state_store.rs	77.55%	2 Missing and 9 partials ⚠️
crates/matrix-sdk/src/room/mod.rs	88.46%	0 Missing and 3 partials ⚠️
crates/matrix-sdk-base/src/store/mod.rs	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5455      +/-   ##
==========================================
+ Coverage   88.88%   88.90%   +0.01%     
==========================================
  Files         333      333              
  Lines       92082    92228     +146     
  Branches    92082    92228     +146     
==========================================
+ Hits        81850    81993     +143     
+ Misses       6403     6393      -10     
- Partials     3829     3842      +13     

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[stefanceriu]

Nice, lgtm 👍