refactor(util, executor): optimize payload handling and schema processing

- Replaced repetitive string operations with a centralized `escapeGJSONPathKey` function.
- Streamlined handling of JSON schema cleaning for Gemini and Antigravity requests.
- Improved payload management by transitioning from byte slices to strings for processing.
- Removed unnecessary cloning of byte slices in several places.

internal/util/gemini_schema.go

@@ -667,6 +667,9 @@ func orDefault(val, def string) string {
 }
 
 func escapeGJSONPathKey(key string) string {
+	if strings.IndexAny(key, ".*?") == -1 {
+		return key
+	}
 	return gjsonPathKeyReplacer.Replace(key)
 }