Try to address WPT running OOM

- Continue to reuse the Browser/Env/Isolate, but no start a new session per test.
- Test http server now properly closes the sendFile fd
- Run WPT in ReleaseMode
- Add --quiet option to WPT and some commented out debug code for dumping v8
  memory stats

.github/workflows/wpt.yml

@@ -30,7 +30,7 @@ jobs:
       - uses: ./.github/actions/install
 
       - name: json output
-        run: zig build wpt -- --json > wpt.json
+        run: zig build -Doptimize=ReleaseFast wpt -- --json > wpt.json
 
       - name: write commit
         run: |