Replace Network Package Type Macros with NS_ENUM

• Group PACKAGE_TYPE_XXX macros into NetworkPackageType NS_TYPED_ENUM
• Specify nullability for NetworkPackage and document potential bugs
• Fixed a bug where the initial battery status of paired devices are not reported

Known Issues

• Enabled plugin settings are not persisted, but this issue is not introduced by this MR.
• The Swift interface for the plugin system is still not optimum. You can read more about some potential future directions at https://invent.kde.org/apollozhu/kdeconnect-ios/-/wikis/Refactor-Plugins