feat: Optimize message list node lookup

[jamesarich]

Pre-calculate a map of nodes for O(1) lookup within the message list items. This avoids an O(N) linear search for each item during scrolling, improving performance.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.57%. Comparing base (f322660) to head (1402dbb).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
...g/meshtastic/feature/messaging/MessageListPaged.kt	0.00%	6 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main   #3981      +/-   ##
========================================
+ Coverage   0.52%   0.57%   +0.04%     
========================================
  Files        395     401       +6     
  Lines      23172   23692     +520     
  Branches    2944    3042      +98     
========================================
+ Hits         122     136      +14     
- Misses     23029   23535     +506     
  Partials      21      21              

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