feat: use standard list item sizes for conversations

[naveensingh]

Type of change(s)

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

What changed and why

• Updated the main list to use standard sizes as per https://m3.material.io/components/lists/specs
  • Reduced avatar size from 56dp to 40dp
  • Reduced primary text size from 18sp to 16sp
  • Updated the layout to use 16dp horizontal and 8dp vertical paddings
  • Updated the gap between elements to 16dp
  • Enforced minimum height of 72dp
• Moved conversation datetime to the top-right corner, as done in other messaging apps
• Moved the pin indicator icon to the bottom right corner and reduced alpha to 0.7f
• Flattened the nested layouts using ConstraintLayout.
• Updated commons to include changes from fix: use standard sizes for contact list item elements commons#219

Tests performed

• Viewing/scrolling conversations
• Conversation pinning/unpinning
• Conversation drafts

Before & after preview

Closes the following issue(s)

• Closes Make message list more compact #376
• Partially addresses Font size cannot auto sync to system preference. General-Discussion#118

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.