Function normalize_cv 

pub fn normalize_cv(cv: f64) -> f64

Normalize coefficient of variation (CV) to [0, 1] using logistic sigmoid.

CV = std / mean of epoch intervals. This ratio is naturally unbounded and heavy-tailed in practice.

The sigmoid is centered at CV=0.5 (moderate regularity) because:

• CV=0 means perfectly regular intervals
• CV=0.5 is typical for many stochastic processes
• CV=1 means std equals mean (high irregularity)
• CV>1 is very irregular (common in financial data)

Special handling: NaN (no epochs) maps to ~0.12, making it distinguishable from real CV values.

Arguments

• cv - Coefficient of variation of epoch intervals (std/mean)

Returns

Normalized value in (0, 1)