tests: use the same browser instance across tests and better use explicit resource management (#2901)

On my machine, reduces time taken to perform `deno task test` from
~1m20s to ~30s.

Inspired by and supersedes #2110.

---------

Co-authored-by: Marvin Hagemeister <marvin@deno.com>

Author: iuioiua

deno.json

@@ -67,7 +67,7 @@
     "@std/semver": "jsr:@std/semver@1",
     "@std/streams": "jsr:@std/streams@1",
 
-    "@astral/astral": "jsr:@astral/astral@^0.5.2",
+    "@astral/astral": "jsr:@astral/astral@^0.5.3",
     "@marvinh-test/fresh-island": "jsr:@marvinh-test/fresh-island@^0.0.1",
     "linkedom": "npm:linkedom@^0.18.10",
     "@std/async": "jsr:@std/async@^1.0.13",