fix: ensure unique call log items to prevent crashes

[naveensingh]

Type of change(s)

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

What changed and why

• Recent calls are now always de-duplicated and sorted after fetch in RecentsHelper. This prevents duplicated calls and date headers due to non-contiguous blocks in the list.
• Search results are now sorted by dayCode ➜ then by startsWith(). This ensures proper sorting and also prevents date header duplication in search results.
• Replaced RecentCall.getDayCode() with an init time property for slightly better performance.

Closes the following issue(s)

• Closes App crashes when putting an b or c in the search bar #378

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).
• All checks are passing.