[Bug]: bidi reports transfer size as responseBodySize, so request().sizes() over-reports the body by the header size

### Version

1.64.0-next, `d1ead3ecc`. Chrome 141 over `--project=bidi-chrome-page`.

### Steps to reproduce

Serve a body of a known length and read `sizes()`:

```js
server.setRoute('/fixed', (req, res) => {
const plain = 'x'.repeat(2000);
res.writeHead(200, { 'content-type': 'text/plain', 'content-length': String(plain.length) });
res.end(plain);
});
const resp = await page.goto(server.PREFIX + '/fixed');
console.log(await resp.request().sizes());
```

### Expected

`responseBodySize` of 2000, as chromium over CDP reports:

```
chromium (CDP) {"requestBodySize":0,"requestHeadersSize":674,"responseBodySize":2000,"responseHeadersSize":151}
```

### Actual

```
bidi-chrome {"requestBodySize":0,"requestHeadersSize":343,"responseBodySize":2151,"responseHeadersSize":132}
```

2151 for a 2000 byte body. That number is exactly CDP's body plus CDP's header size (2000 + 151), so what is coming back is the whole transfer, headers included, in the body field. Same overshoot on the other shapes I tried: a gzipped body whose encoded length is 35 reports 208, and a chunked response whose wire body is 15 reports 172.

### Cause

`packages/playwright-core/src/server/bidi/bidiNetworkManager.ts:168`:

```ts
response.setTransferSize(params.response.bodySize);
response.setEncodedBodySize(params.response.bodySize);
```

One protocol field feeds two different metrics. The codebase treats them as distinct, and `network.ts:719` spells the relationship out in the fallback path:

```ts
transferSize = responseHeadersSize + encodedBodySize;
```

so setting both from one value cannot be right for both. CDP keeps them apart:

```ts
response.setTransferSize(event.encodedDataLength);
response.responseHeadersSize().then(size => response.setEncodedBodySize(event.encodedDataLength - size));
```

WebKit only sets `setEncodedBodySize(event.metrics?.responseBodyBytesReceived)` and leaves transfer size to the fallback.

If BiDi's `network.ResponseData` carries `headersSize` alongside `bodySize`, subtracting it the way CDP does would line the two up. I did not check what Chrome actually populates there, so that part is a suggestion rather than a diagnosis.

### Scope

Only the bidi backend, which I realise is still experimental and tracked under #32577, so this is a low-priority one. Filing it discretely because the value is plainly wrong rather than merely missing, and the cause is two lines.

I am a freshman in college doing my best to contribute usefully, so if bidi gaps are better collected on #32577 than filed one by one, tell me and I will move it there.

Start in packages/playwright-core/src/server/bidi/bidiNetworkManager.ts:168, then compare the fallback relationship in network.ts:719 and the CDP handling described in the issue. Inspect whether BiDi Network.ResponseData provides headersSize alongside bodySize. Done means request().sizes() reports the 2000-byte body separately from response headers for the reproduction and other response shapes.

Written by the indexing model from the issue text.