High Volume Bars (Improved)

Highlights high-volume bars using absolute, delta, or z-score modes.
Shows optional volume bands in a separate pane; barcolor/bgcolor still affect the main chart.

Inputs:

• lookback length
  
• stddev multiplier
  
• change vs z-score modes
  
• SMA/EMA smoothing
  
• optional background highlight, and band visibility.
  

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