chore: import upstream snapshot with attribution

pkg/http/headers/parse.go

@@ -0,0 +1,21 @@
+package headers
+
+import "strings"
+
+// ParseCommaSeparated splits a header value by comma, trims whitespace,
+// and filters out empty values
+func ParseCommaSeparated(value string) []string {
+	if value == "" {
+		return []string{}
+	}
+
+	parts := strings.Split(value, ",")
+	result := make([]string, 0, len(parts))
+	for _, p := range parts {
+		trimmed := strings.TrimSpace(p)
+		if trimmed != "" {
+			result = append(result, trimmed)
+		}
+	}
+	return result
+}