feat: 15 funciones finance — indicadores, riesgo e IO de mercado

11 funciones puras con implementación real:
SMA, EMA, RSI, BollingerBands, VWAP, LogReturn, AnnualizedVolatility,
SharpeRatio, MaxDrawdown, NormalizeOHLCV, TickToOHLCV

4 funciones impuras (stubs):
FetchOHLCV, StreamTicks, WriteOHLCVToParquet, LoadOHLCVFromDuckDB

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

functions/finance/sma.go

@@ -0,0 +1,22 @@
+package finance
+
+// SMA calcula la media movil simple de data con el periodo dado.
+// Retorna un slice de longitud len(data) donde los primeros period-1
+// elementos son 0 (sin datos suficientes).
+func SMA(data []float64, period int) []float64 {
+	n := len(data)
+	result := make([]float64, n)
+	if period <= 0 || period > n {
+		return result
+	}
+	var sum float64
+	for i := 0; i < period; i++ {
+		sum += data[i]
+	}
+	result[period-1] = sum / float64(period)
+	for i := period; i < n; i++ {
+		sum += data[i] - data[i-period]
+		result[i] = sum / float64(period)
+	}
+	return result
+}