This commit introduces a new field `main_screen_type` to the `UserPreferences` proto and updates `UserPreferencesRepository` to support managing the main screen's data type.

- Added `main_screen_type` (int64) to `user_preferences.proto`.
- Updated `UserPreferencesRepository` to map the stored `main_screen_type` integer to the corresponding `MainData` sealed class (Note, Achieve, Trash, Remainder, Label).
- Added `setMainData` function to `UserPreferencesRepository` to update the `main_screen_type` in DataStore.

Added a new field `mainData` to the `MainActivityUiState` data class in `SharedActivityViewModel.kt`. This field is of type `MainData` and defaults to `MainData.Note`.

The `mainData` field will be used to determine which main screen content to display (e.g., Notes, Labels).

Added a trailing comma to the `mainData` property in the `UserData` data class. This is a stylistic change for consistency.

Also, removed an extra newline from the end of `MainData.kt`.

The `setMainData` function in `UserPreferencesRepository.kt` now accepts a `Long` parameter named `index` instead of a `MainData` object.

The function's implementation was updated to directly use the `index` parameter when setting the `mainScreenType` in user preferences.

This commit introduces a new function `setMainData(mainData: Long)` to the `UserDataRepository` interface and its implementation `OfflineFirstUserDataRepository`.

This function allows setting a `Long` value, presumably related to main application data, which is then stored via the `userPreferencesRepository`.

- Added `suspend fun setMainData(mainData: Long)` to `UserDataRepository.kt`
- Implemented `setMainData` in `OfflineFirstUserDataRepository.kt` to call `userPreferencesRepository.setMainData(mainData)`

Removed the `TypeArg` navigation argument from `MainRoute`. The `MainViewModel` now retrieves the main data type from `UserDataRepository` instead of `SavedStateHandle`.

This change simplifies the navigation to `MainScreen` and centralizes the logic for determining the content to display.

Files affected:
- `feature/main/src/main/kotlin/com/mshdabiola/main/navigation/MainNavigation.kt`
- `feature/main/src/main/kotlin/com/mshdabiola/main/MainViewModel.kt`

This commit introduces changes to how main data (e.g., Note, Checklist) is handled and improves navigation within the application.

- Modified `SharedActivityViewModel` to correctly initialize `mainData` in `UserData`.
- Added `setMainData` function to `MainActivityViewModel` to allow updating the main data type (Note or Checklist) in `UserDataRepository`.
- Updated `NoteApp` to:
    - Use `uiState` from `MainActivityViewModel` to determine the current `mainData` for the `MainNavigation` drawer.
    - Call `viewModel.setMainData(it)` when a navigation item in the drawer is selected.
    - Navigate to the main screen without passing the type argument, as this is now handled by `setMainData`.
- Removed the `mainArg` property from `NoteAppState` as it's no longer needed for determining the main screen's content type.

When a label is deleted in `LabelViewModel`, the `userDataRepository.setMainData` method is now called with `MainData.Note.index`. This ensures that the main screen is updated to reflect the change, likely by navigating to the notes screen.

Modified `SharingStarted.WhileSubscribed` in `MainActivityViewModel.kt` to remove the 5-second timeout.
Removed unused imports `TypeArg` and `NoteType` from `NoteAppState.kt`.

- `SharingStarted.WhileSubscribed(5_000)` -> `SharingStarted.WhileSubscribed()` in `MainActivityViewModel.kt`

Removed the unused import `com.mshdabiola.model.NoteType` from `UserPreferencesRepository.kt`.

This commit refactors the `MainViewModel.kt` file.

- Removed unused imports: `SharingStarted` and `stateIn`.
- Simplified conditional logic for updating `_mainState.value` based on `userDataRepository.userData`.
- Streamlined the logic for initializing `_mainState.value` within the `init` block by directly checking the current state.

Removed the `androidx.navigation.navOptions` import from `NoteApp.kt` as it was no longer needed.

This commit adds the `setMainData` method to `FakeUserDataRepository` and `TestUserDataRepository`.

- In `FakeUserDataRepository`, `setMainData` now calls the corresponding method in `userPreferencesRepository`.
- In `TestUserDataRepository`, `setMainData` updates the `mainData` field of the current `UserData` to `MainData.Note` and emits the updated data.
- The initial `UserData` in `TestUserDataRepository` now includes `mainData = MainData.Note`.

Updated the `MainData.Label` class to use its `id` property as its `index`. Previously, it was hardcoded to `0L`.

- `MainData.Label(val id: Long) : MainData(0L)` -> `MainData.Label(val id: Long) : MainData(index = id)` in `MainData.kt`

This commit removes several unused files related to data migrations and data classes from the `datastore` module.

- Deleted `ChangeListVersions.kt`.
- Deleted `IntToStringIdsMigration.kt` and its corresponding test file `IntToStringIdsMigrationTest.kt`.
- Deleted `ListToMapMigrationTest.kt`.
- Removed `IntToStringIdsMigration` from the `DataStoreModule.kt` as it's no longer needed.

This commit updates `OfflineFirstUserDataRepositoryTest.kt` to include `mainData` in the `UserData` initialization.

- Added `MainData.Label(0)` as the initial value for the `mainData` property in the `UserData` object within the test setup.