Fix connection pool reuse: HTTP/1.1 is persistent by default (RFC 7230)

[owner888]

What

Fix connection pool reuse: treat HTTP/1.1 connections as persistent by default (RFC 7230 §6.3), instead of requiring both request and response to carry an explicit Connection: keep-alive header.

Why

recycleConnectionFromRequest() currently closes the connection unless both sides literally sent Connection: keep-alive:

if ('keep-alive' !== $request_header_connection || 'keep-alive' !== $response_header_connection || ...) {
    $connection->close();
}

Real-world HTTP/1.1 servers (nginx, Google frontends, most CDNs) omit the Connection header because persistence is the protocol default. As a result the pool closes every connection after each response and never actually reuses any — every request pays a fresh TCP + TLS handshake.

Per RFC 7230 §6.3, an HTTP/1.1 connection persists unless either side explicitly signals close.

Benchmark

Streaming requests against generativelanguage.googleapis.com (20 samples each, time-to-first-byte):

	median	min
before (no reuse, handshake every request)	0.934s	0.821s
after this fix	0.803s	0.645s

~130ms saved per request once the pool warms up.

Notes

• Transport-level failures (no response) and non-1.1 protocols still close the connection, as before.
• If a server does close the socket unilaterally, process() already handles it via the existing getStatus() → reconnect() path, so pooling a to-be-closed connection is safe.