feat: migrate from Melos to Dart pub workspaces

[myConsciousness]

• Remove melos.yaml configuration file
• Add workspace configuration to root pubspec.yaml
• Add 'resolution: workspace' to all package pubspec.yaml files
• Remove all pubspec_overrides.yaml files from packages
• Update build scripts to work with pub workspaces
• Remove codecov.yaml (no longer needed)
• Update coverage script to remove melos-specific commands

This migration simplifies dependency management by using Dart's native pub workspaces feature instead of the external Melos tool.