Do not apply chunked encoding to 204/304 responses

[DmitryBoiadji]

Http1Driver special-cases HEAD requests but not bodyless status codes: a 204 or 304 response without a content-length header gets transfer-encoding: chunked and the 0\r\n\r\n terminator.

RFC 9112 §6.1: "A server MUST NOT send a Transfer-Encoding header field in any response with a status code of 1xx (Informational) or 204 (No Content)." Per §6.3, clients terminate 204/304 responses at the end of the header section regardless of framing headers - so the terminator bytes stay in the socket and are parsed as the start of the next response, killing the next request on the keep-alive connection. Observed against Chrome: every CORS preflight (204) poisoned its connection and the following fetch failed with a network error.

A bare new Response(204) is unaffected (setBody('') sets content-length: 0), but passing any header array to the constructor makes setHeaders() replace all headers, dropping the auto-set content-length - which is how adapters that copy headers from another response object hit this.

The fix excludes 204/304 from chunked encoding and skips the body write the same way HEAD requests already do. Setting $need = null in that branch also stops the finally block from treating the intentionally unwritten body as a truncated write and abruptly closing the connection (previously reachable with a HEAD response carrying a content-length).

Repro (v3.4.6, PHP 8.4):

$server = SocketHttpServer::createForDirectAccess(new NullLogger());
$server->expose('127.0.0.1:1337');
$server->start(
    new ClosureRequestHandler(fn () => new Response(204, ['x-demo' => '1'])),
    new DefaultErrorHandler(),
);

$ printf 'GET / HTTP/1.1\r\nHost: l\r\nConnection: keep-alive\r\n\r\n' | nc 127.0.0.1 1337
HTTP/1.1 204 No Content
x-demo: 1
connection: keep-alive
keep-alive: timeout=15
transfer-encoding: chunked

0        <- stray bytes; a compliant client stops reading at the blank line above

The three added tests fail on 3.x without the driver change and pass with it; the rest of the suite, composer code-style and Psalm are unaffected.