refactor: deduplicate numericOnly and DuckDuckGo result extraction

- Extract identical numericOnly inline functions from powerball and
  megamillions into shared sites/internal/parse.NumericOnly with tests
- Extract duplicated DuckDuckGo result parsing from Search() and
  GetResults() into shared extractResults() helper

Closes #13, #14

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sites/internal/parse/parse.go

@@ -0,0 +1,21 @@
+package parse
+
+import "strconv"
+
+// NumericOnly extracts only digits and decimal points from a string and
+// returns the result as a float64. Returns 0 if parsing fails.
+func NumericOnly(in string) float64 {
+	var out string
+	for _, r := range in {
+		if (r >= '0' && r <= '9') || r == '.' {
+			out += string(r)
+		}
+	}
+
+	val, err := strconv.ParseFloat(out, 64)
+	if err != nil {
+		return 0
+	}
+
+	return val
+}