refactor: simplify test helper using stdlib strings.Contains

Addresses code review feedback from silverwind:
- Replace complex custom contains() implementation with strings.Contains
- Remove unnecessary containsMiddle() function
- Improves readability and maintainability by using standard library

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

pkg/params/params_test.go

@@ -1,6 +1,7 @@
 package params
 
 import (
+	"strings"
 	"testing"
 )
 
@@ -103,14 +104,5 @@ func TestGetIndex(t *testing.T) {
 }
 
 func contains(s, substr string) bool {
-	return len(s) >= len(substr) && (s == substr || len(s) > len(substr) && (s[:len(substr)] == substr || s[len(s)-len(substr):] == substr || containsMiddle(s, substr)))
-}
-
-func containsMiddle(s, substr string) bool {
-	for i := 0; i <= len(s)-len(substr); i++ {
-		if s[i:i+len(substr)] == substr {
-			return true
-		}
-	}
-	return false
+	return strings.Contains(s, substr)
 }