Volume Z-Score

// This indicator calculates the Z-Score of trading volume to identify
// statistically significant volume spikes. It uses a dynamic percentile-based
// threshold to highlight extreme volume events.
//
// How it works:
// - Z-Score measures how many standard deviations the current volume is from the mean
// - The threshold line represents the top 1% (99th percentile) of historical Z-Score values
// - When volume Z-Score exceeds the threshold, the line turns red
//
// Use cases:
// - Spot unusual institutional activity or large block trades
// - Identify potential breakout or breakdown points with volume confirmation
// - Filter out noise by focusing only on statistically extreme volume events
//
// Parameters:
// - Period Length: Lookback period for calculating mean and standard deviation
// - Percentile Threshold: Defines the extreme volume cutoff (default 99 = top 1%)
// ===================================