Implement robust one/two-sided p-value function

Below is a complete implementation of the requested p_value function. It uses only math.erf/math.erfc for the standard normal case and scipy.stats.t when available, falling back to a continued‑fraction incomplete beta implementation otherwise. Numerical Stability for Small p-values The implementation avoids subtracting a value close to 1 from 1, which is the main source of catastrophic cancellation for tiny tail probabilities. Standard normal: For a greater alternative with…