Add last page detection to stop unnecessary API calls

[jlkim909]

🎯 Goal

This PR fixes an issue where additional network requests were being made on the Home screen even after reaching the last page of the Pokémon API.
Unnecessary fetches are now prevented once the end of the list is reached.

🛠 Implementation details

• Added an onLastPageReached: () -> Unit callback to HomeRepository.fetchPokemonList.
• When the next field in the Pokémon API response is null, indicating the last page, onLastPageReached() is called.
• In HomeViewModel, this callback sets an internal isLastPageReached flag to true.
• fetchNextPokemonList() checks this flag to determine whether to initiate another fetch.
• This ensures that no further network calls are made after the final page, preventing redundant data loading.

✍️ Explain examples

// HomeRepositoryImpl.kt
if (data.next == null) {
    onLastPageReached() // Last page reached
}

// HomeViewModel.kt
fun fetchNextPokemonList() {
    if (uiState.value != HomeUiState.Loading && !isLastPageReached) {
        pokemonFetchingIndex.value++
    }
}

Screenshot

[skydoves]

I've never thought about the last page detection 😄 This makes sense and thank you for your contribution! Just small comments.