feat: 15 funciones datascience — estadística, DSP e IO de datos

12 funciones puras con implementación real:
Standardize, MinMaxScale, Clip, RollingWindow, ZipSlices, GroupBy,
Histogram, Pearson, Autocorrelation, FFT (Cooley-Tukey), DetectOutliers, Impute

3 funciones impuras (stubs):
LoadCSV, LoadParquet, FetchDataFrame

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

functions/datascience/min_max_scale.go

@@ -0,0 +1,33 @@
+package datascience
+
+import "math"
+
+// MinMaxScale escala los valores al rango [0, 1] usando min-max normalización.
+// Si min == max, retorna un slice de ceros.
+func MinMaxScale(data []float64) []float64 {
+	n := len(data)
+	if n == 0 {
+		return []float64{}
+	}
+
+	minVal := math.Inf(1)
+	maxVal := math.Inf(-1)
+	for _, v := range data {
+		if v < minVal {
+			minVal = v
+		}
+		if v > maxVal {
+			maxVal = v
+		}
+	}
+
+	rang := maxVal - minVal
+	result := make([]float64, n)
+	if rang == 0 {
+		return result
+	}
+	for i, v := range data {
+		result[i] = (v - minVal) / rang
+	}
+	return result
+}