Enhance SaveImage functionality with custom prompt support

- Added a new optional parameter `custom_prompt` to the SaveImage class methods to allow users to override the default prompt.
- Updated the `format_metadata` method to utilize the custom prompt if provided.
- Modified the `save_images` and `process_image` methods to accept and pass the custom prompt through the workflow processing.

py/workflow/mappers.py

@@ -134,7 +134,7 @@ def transform_lora_loader(inputs: Dict) -> Dict:
         "loras": " ".join(lora_texts)
     }
 
-    if "clip" in inputs:
+    if "clip" in inputs and isinstance(inputs["clip"], dict):
         result["clip_skip"] = inputs["clip"].get("clip_skip", "-1")
     
     return result