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/rsi.go

@@ -0,0 +1,47 @@
+package finance
+
+// RSI calcula el Relative Strength Index.
+// Usa el metodo de suavizado de Wilder (EMA con alpha = 1/period).
+// Los primeros period elementos del resultado son 0.
+func RSI(data []float64, period int) []float64 {
+	n := len(data)
+	result := make([]float64, n)
+	if period <= 0 || n < period+1 {
+		return result
+	}
+	var gainSum, lossSum float64
+	for i := 1; i <= period; i++ {
+		change := data[i] - data[i-1]
+		if change > 0 {
+			gainSum += change
+		} else {
+			lossSum -= change
+		}
+	}
+	avgGain := gainSum / float64(period)
+	avgLoss := lossSum / float64(period)
+	if avgLoss == 0 {
+		result[period] = 100
+	} else {
+		rs := avgGain / avgLoss
+		result[period] = 100 - 100/(1+rs)
+	}
+	for i := period + 1; i < n; i++ {
+		change := data[i] - data[i-1]
+		var gain, loss float64
+		if change > 0 {
+			gain = change
+		} else {
+			loss = -change
+		}
+		avgGain = (avgGain*float64(period-1) + gain) / float64(period)
+		avgLoss = (avgLoss*float64(period-1) + loss) / float64(period)
+		if avgLoss == 0 {
+			result[i] = 100
+		} else {
+			rs := avgGain / avgLoss
+			result[i] = 100 - 100/(1+rs)
+		}
+	}
+	return result
+}