perf: lazy header instantiation for HTTP requests (#10150)

This commit introduces a performance optimization for the native HTTP
server. From my testing it is about 2-6% faster than `main`. Request
headers in the HTTP servers are now lazilly instatated when they are
accessed, rather than being preemptively wrapped in the `Headers` class.

1 files changed, 3 insertions, 2 deletions

diff --git a/runtime/js/40_http.js b/runtime/js/40_http.js
index 4a2dcdf4a..18ead84c3 100644
--- a/runtime/js/40_http.js
+++ b/runtime/js/40_http.js
@@ -2,7 +2,7 @@
 "use strict";
 
 ((window) => {
-  const { Request, dontValidateUrl, fastBody, Response } =
+  const { Request, dontValidateUrl, lazyHeaders, fastBody, Response } =
     window.__bootstrap.fetch;
   const { Headers } = window.__bootstrap.headers;
   const errors = window.__bootstrap.errors.errors;
@@ -61,8 +61,9 @@
       const request = new Request(url, {
         body,
         method,
-        headers: new Headers(headersList),
+        headers: headersList,
         [dontValidateUrl]: true,
+        [lazyHeaders]: true,
       });
 
       const respondWith = createRespondWith(responseSenderRid, this.#rid);