refactor(magic_pdf): import model helpers directly for clarity

Update import statements in `pdf_parse_union_core_v2.py` to directly import
`prepare_inputs`, `boxes2inputs`, and `parse_logits` from `magic_pdf.model.v3.helpers`
instead of from `magic_pdf.model.v3`. This change streamlines the imports, making the
code more readable and maintaining a cleaner approach to modular design.

magic_pdf/pdf_parse_union_core_v2.py

@@ -140,7 +140,7 @@ class ModelSingleton:
 
 
 def do_predict(boxes: List[List[int]], model) -> List[int]:
-    from magic_pdf.model.v3 import prepare_inputs, boxes2inputs, parse_logits
+    from magic_pdf.model.v3.helpers import prepare_inputs, boxes2inputs, parse_logits
     inputs = boxes2inputs(boxes)
     inputs = prepare_inputs(inputs, model)
     logits = model(**inputs).logits.cpu().squeeze(0)