feat: add mapping functions

internal/author/mapper.go

@@ -0,0 +1,21 @@
+package author
+
+import "tutorial.sqlc.dev/app/internal/author/gen"
+
+func toAuthor(a gen.Author) Author {
+	return Author{
+		a.ID, a.Name, a.Bio.String,
+	}
+}
+
+func mapSlice[K any, V any](conv func(K) V) func([]K) []V {
+	return func(inputs []K) []V {
+		output := make([]V, len(inputs))
+		for i, input := range inputs {
+			output[i] = conv(input)
+		}
+		return output
+	}
+}
+
+var toAuthorSlice = mapSlice(toAuthor)