perf: optimize loading messages in threads

[naveensingh]

Type of change(s)

• Bug fix
• Feature / enhancement
• Infrastructure / tooling (CI, build, deps, tests)
• Documentation

What changed and why

1. Removed the endless scroll listener in favor of early prefetch based on user scroll. This queues a next page load as soon as the number of remaining messages is found to be less than the specified threshold.
2. Introduced a simple cache mechanism for getNameAndPhotoFromPhoneNumber() and getThreadParticipants(). The original code was inefficiently querying these values for every message in the thread. Caching the results cut loading time by 50%.
3. Removed eager dimension reading for attachments when loading MMS messages, as Gilde does it fine without any performance overhead. This was the main reason threads containing MMS messages were slow to load, even with early prefetch from 1.
4. Removed the circular loading indicator that appeared when the next page was being loaded because it's no longer necessary after 1, 2 & 3.
5. Increased the initial message load count from 30 to 50. It won't lead to slower initial loads because of the optimizations above. Originally, it was 100, but it was reduced to 30 to workaround existing inefficiencies in the code (Slow rendering when lots of messages for a contact SimpleMobileTools/Simple-SMS-Messenger#44).
6. Updated the thread adapter code to use actual stable IDs instead of hash codes.

Tests performed

• Sending & receiving SMS messages
• Sending & receiving MMS messages
• Scrolling fast/slow to the very top/bottom of the thread
• Deleting messages

According to testing on two of my phones, loading is now 4 times faster compared to v1.4.0.

Closes the following issue(s)

• Partially addresses Slow performance when loading conversations and messages #234
• These changes improve general UX and should also help with When selecting a search result, take me to where that message is in the conversation instead of the latest #350. Messages take long time to appear #123 is a related issue.

Checklist

• I read the contribution guidelines.
• I manually tested my changes on device/emulator (if applicable).
• I updated the "Unreleased" section in CHANGELOG.md (if applicable).
• I have self-reviewed my pull request (no typos, formatting errors, etc.).
• All checks are passing.