feat(sdk): Add ThreadInfo with its own ReadReceipts

[Hywan]

These patches add the ability to compute ReadReceipts for thread. It does several things (in logical order):

• It creates the new:

  struct ThreadInfo {
      read_receipts: ReadReceipts,
  }

• It updates the threads table to add a new info column/field,
• It updates EventCacheStore to remove remember_thread and to add load_thread_info and update_thread_info,
• It makes event_cache::read_receipts::compute_unread_counts “timeline agnostic” so that it supports both room and thread,
• It updates ThreadEventCache::handle_timeline to receive ephemeral events (which include the read receipt events),
• It combines all that to compute the read receipts for threads!

Tasks

• Write more tests

---

• Stacked on top of feat(sdk): ThreadEventCache's pagination and in-memory UTD resolution post-process upserted events #6888, waiting to be merged.
• Related to Event cache: handle read receipts and unread counts #4113.

---

• I've documented the public API changes in the appropriate changelog files (see Writing changelog entries).
• This PR was made with the help of AI.

Signed-off-by:

[codecov]

Codecov Report

❌ Patch coverage is 92.26804% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.08%. Comparing base (b479a6f) to head (bff5d12).
⚠️ Report is 7 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
.../matrix-sdk/src/event_cache/caches/thread/state.rs	82.60%	4 Missing and 4 partials ⚠️
crates/matrix-sdk-sqlite/src/event_cache_store.rs	82.50%	1 Missing and 6 partials ⚠️
...matrix-sdk/src/event_cache/caches/read_receipts.rs	98.05%	3 Missing and 2 partials ⚠️
crates/matrix-sdk-common/src/serde_helpers.rs	75.00%	3 Missing ⚠️
...es/matrix-sdk/src/event_cache/caches/thread/mod.rs	75.00%	2 Missing and 1 partial ⚠️
crates/matrix-sdk/src/event_cache/redecryptor.rs	0.00%	2 Missing ⚠️
...es/matrix-sdk/src/event_cache/caches/room/state.rs	83.33%	0 Missing and 1 partial ⚠️
...ix-sdk/src/event_cache/caches/thread/pagination.rs	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6893      +/-   ##
==========================================
- Coverage   90.10%   90.08%   -0.02%     
==========================================
  Files         407      408       +1     
  Lines      115745   115976     +231     
  Branches   115745   115976     +231     
==========================================
+ Hits       104294   104481     +187     
- Misses       7540     7562      +22     
- Partials     3911     3933      +22     

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[codspeed-hq]

Merging this PR will not alter performance

✅ 28 untouched benchmarks
⏩ 22 skipped benchmarks¹

---

_{Comparing Hywan:feat-sdk-event-cache-thread-read-receipt (df54bb0) with main (8c9144d)}

Footnotes

1. 22 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩