feat: 16 funciones cybersecurity — análisis, crypto e IO de seguridad

12 funciones puras con implementación real:
HashSHA256, HashMD5, EntropyShannon, IsBase64, IsHex, ExtractURLs,
ParseIPCIDR, IPInRange, NormalizeURL, DetectSQLInjection,
LevenshteinDistance, JaccardSimilarity

4 funciones impuras con implementación real (stdlib):
LookupWhois, ResolveDNS, FetchHTTPHeaders, ScanPortTCP

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

functions/cybersecurity/levenshtein_distance.go

@@ -0,0 +1,49 @@
+package cybersecurity
+
+// LevenshteinDistance calcula la distancia de edicion (Levenshtein) entre dos strings.
+func LevenshteinDistance(a, b string) int {
+	ra := []rune(a)
+	rb := []rune(b)
+	la := len(ra)
+	lb := len(rb)
+
+	if la == 0 {
+		return lb
+	}
+	if lb == 0 {
+		return la
+	}
+
+	// Usar solo dos filas para optimizar memoria
+	prev := make([]int, lb+1)
+	curr := make([]int, lb+1)
+
+	for j := 0; j <= lb; j++ {
+		prev[j] = j
+	}
+
+	for i := 1; i <= la; i++ {
+		curr[0] = i
+		for j := 1; j <= lb; j++ {
+			cost := 1
+			if ra[i-1] == rb[j-1] {
+				cost = 0
+			}
+			del := prev[j] + 1
+			ins := curr[j-1] + 1
+			sub := prev[j-1] + cost
+
+			m := del
+			if ins < m {
+				m = ins
+			}
+			if sub < m {
+				m = sub
+			}
+			curr[j] = m
+		}
+		prev, curr = curr, prev
+	}
+
+	return prev[lb]
+}