perf(http): make heap allocation for path conditional (#26289)

Code:

```js
Deno.serve({ port: 8085 }, request => {
  return new Response(request.url);
});
```

Before:

```
% wrk -d60s http://localhost:8085/path/testing\?testing=5
Running 1m test @ http://localhost:8085/path/testing?testing=5
  2 threads and 10 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency    56.01us   18.34us   3.28ms   93.84%
    Req/Sec    81.80k     3.13k   88.26k    90.77%
  9783713 requests in 1.00m, 1.67GB read
Requests/sec: 162789.89
Transfer/sec:     28.41MB
```

After:

```
% wrk -d60s http://localhost:8085/path/testing\?testing=5
Running 1m test @ http://localhost:8085/path/testing?testing=5
  2 threads and 10 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency    55.44us   15.20us   2.42ms   90.41%
    Req/Sec    82.71k     2.92k   88.10k    89.93%
  9892916 requests in 1.00m, 1.69GB read
Requests/sec: 164607.06
Transfer/sec:     28.73MB
```

0 files changed, 0 insertions, 0 deletions