Cut a Flow into chunks for batch processing.

Flow.chunked.kt

import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
import kotlinx.coroutines.flow.*

fun <T> Flow<T>.chunked(size: Int): Flow<List<T>> = flow {
    val elements = ArrayList<T>(size)
    collect {
        elements.add(it)
        if (elements.size == size) {
            emit(elements.toList())
            elements.clear()
        }
    }
    if (elements.isNotEmpty()) emit(elements)
}