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/powerball/powerball.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"gitea.stevedudenhoeffer.com/steve/go-extractor"
+	"gitea.stevedudenhoeffer.com/steve/go-extractor/sites/internal/parse"
 )
 
 type Config struct {
@@ -144,30 +145,7 @@ func getNextDrawing(_ context.Context, doc extractor.Document) (*NextDrawing, er
 
 	// jackpot is in the format of "$1.5 billion", "$100 million", or "$200,000" etc
 
-	// make one filter to only get the numeric part of the jackpot
-
-	numericOnly := func(in string) float64 {
-		var out string
-		for _, r := range in {
-			if r >= '0' && r <= '9' {
-				out += string(r)
-			}
-
-			if r == '.' {
-				out += string(r)
-			}
-		}
-
-		val, err := strconv.ParseFloat(out, 64)
-
-		if err != nil {
-			return 0
-		}
-
-		return val
-	}
-
-	numeric := numericOnly(txt)
+	numeric := parse.NumericOnly(txt)
 
 	if strings.Contains(txt, "Billion") {
 		nextDrawing.JackpotDollars = int(numeric * 1000000000)