improve cookie handling by ensuring cookies are properly typed and refactor data event listener for consistency

src/index.ts

@@ -112,11 +112,12 @@ export default class Flummpress {
       searchParams: url.searchParams,
       qs: Object.fromEntries(url.searchParams.entries()),
     };
+
     req.cookies = {};
     if(req.headers.cookie) {
       req.headers.cookie.split("; ").forEach(cookie => {
         const [key, value] = cookie.split("=");
-        req.cookies[key] = decodeURIComponent(value);
+        req.cookies![key] = decodeURIComponent(value);
       });
     }
   }
@@ -130,7 +131,7 @@ export default class Flummpress {
     return new Promise((resolve, reject) => {
       let body = "";
 
-      req.on("data", (chunk) => {
+      req.on("data", chunk => {
         body += chunk;
       });