feat(domain): add core use cases

app/src/main/java/com/radiola/domain/usecase/GetNowPlayingUseCase.kt

@@ -0,0 +1,14 @@
+package com.radiola.domain.usecase
+
+import com.radiola.domain.model.Track
+import com.radiola.domain.repository.NowPlayingRepository
+import kotlinx.coroutines.flow.Flow
+import javax.inject.Inject
+
+class GetNowPlayingUseCase @Inject constructor(
+    private val nowPlayingRepository: NowPlayingRepository
+) {
+    operator fun invoke(stationPrefix: String): Flow<Track?> {
+        return nowPlayingRepository.getNowPlaying(stationPrefix)
+    }
+}