When detecting the format, detect its version as well

There is no need to detect the format and then the version when both can be
done at the same time.

Add a benchmark as well, on large and small atom and rss files.

internal/reader/parser/parser_test.go

@@ -4,10 +4,31 @@
 package parser // import "miniflux.app/v2/internal/reader/parser"
 
 import (
+	"os"
 	"strings"
 	"testing"
 )
 
+func BenchmarkParse(b *testing.B) {
+	var testCases = map[string][]string{
+		"large_atom.xml": {"https://dustri.org/b", ""},
+		"large_rss.xml":  {"https://dustri.org/b", ""},
+		"small_atom.xml": {"https://github.com/miniflux/v2/commits/main", ""},
+	}
+	for filename := range testCases {
+		data, err := os.ReadFile("./testdata/" + filename)
+		if err != nil {
+			b.Fatalf(`Unable to read file %q: %v`, filename, err)
+		}
+		testCases[filename][1] = string(data)
+	}
+	for range b.N {
+		for _, v := range testCases {
+			ParseFeed(v[0], strings.NewReader(v[1]))
+		}
+	}
+}
+
 func FuzzParse(f *testing.F) {
 	f.Add("https://z.org", `<?xml version="1.0" encoding="utf-8"?>
 <feed xmlns="http://www.w3.org/2005/Atom">