add ChunkStrings for splitting a string slice into fixed-size batches

ChunkStrings cuts a slice into consecutive pieces of at most the requested
size, with the leftovers in the last piece, and returns copies so the pieces
cannot disturb each other. Comes with a doc comment and table-driven tests.
(closes #3)

Model: opus-5

chunk.go

@@ -0,0 +1,26 @@
+package util
+
+// ChunkStrings splits input into consecutive slices of at most size elements.
+// The last slice holds whatever is left over and may be shorter than the
+// others. Each returned slice is a copy, so appending to one of them cannot
+// disturb another. A size below one, or an empty input, returns nil.
+func ChunkStrings(input []string, size int) [][]string {
+	if size < 1 || len(input) == 0 {
+		return nil
+	}
+
+	out := make([][]string, 0, (len(input)+size-1)/size)
+
+	for start := 0; start < len(input); start += size {
+		end := start + size
+		if end > len(input) {
+			end = len(input)
+		}
+
+		chunk := make([]string, end-start)
+		copy(chunk, input[start:end])
+		out = append(out, chunk)
+	}
+
+	return out
+}