**Bug: SignUpdateLeverage always returns MarginMode=0 regardless of input**

[zzq0824]

Environment:

• Python version: 3.9.12
• Linux
  The C library function SignUpdateLeverage always generates transaction data with MarginMode: 0 (Cross), even when margin_mode=1 (Isolated) is passed as parameter.
  Expected behavior:
  When margin_mode=1 is passed, the output JSON should contain "MarginMode": 1.
  Actual behavior:
  Output always contains "MarginMode": 0, regardless of input.