fix some typing and add some const

Author: Uzlopak

src/llhttp/constants.ts

@@ -268,13 +268,13 @@ export const METHODS_NON_STANDARD = {
 
   /* DRAFT https://www.ietf.org/archive/id/draft-ietf-httpbis-safe-method-w-body-02.html */
   QUERY: 46,
-}
+} as const;
 
 export const METHODS_ICECAST = {
   SOURCE: 33,
-}
+} as const;
 
-export const METHODS_AIRPLAY: Pick<typeof METHODS_BASIC_HTTP, "GET" | "POST"> = {
+export const METHODS_AIRPLAY: Simplify<Pick<typeof METHODS_BASIC_HTTP, "GET" | "POST">> = {
   GET: 1,
   POST: 3,
 } as const;