HTTP/1.1 server ignores the request's `Connection` header

Related to #53 but this concerns outbound connection lifetimes.

The HTTP1 Server doesn't respect RFC 9112 and doesn't close the connection on a complete response when the client sends a Connection: close in the header. The server should send Connection: close in the response.

Expected behavior

Per RFC 9112 § 9.6, a client sending Connection: close is stating that this is the last request on the connection. The server should close the once the response is complete, and should send Connection: close in the response.

HTTP/1.0 goes against the spec as well and keeps the connection open when it shouldn't.

Root cause

HTTPKeepAliveHandler never reads the inbound Connection header. Its channelRead case .head only resets requestEndReceived / closeAfterResponseEnd, and the only reference to the header in the whole NIOHTTPServer module is a write in the keep alive handler. So the client's request to close isn't accounted for anywhere.

Impact

The connection stays open for the full read-header timeout after the client has said it is finished

Fix

closeAfterResponseEnd does exactly the right thing when response .end is written, we just need to update it to also be set from the request side:

• on .head, read the request's Connection header:
  set closeAfterResponseEnd = true for HTTP/1.1 with Connection: close, and for HTTP/1.0 unless
  Connection: keep-alive is present
• when closing because of that, add Connection: close to the response head

Steps to reproduce

printf 'GET /hello HTTP/1.1\r\nHost: localhost\r\nConnection: close\r\n\r\n' | nc localhost 8080

nc stays connected for ~30s after the response arrives; it should return as soon as the response is
complete.

Environment

• swift-http-server @ 13b8e725554b5d10dbf704f9abc39d7c1c80b30a
• Swift 6.4 development snapshot (2026-08-14), macOS 15 arm64
• Found while adding HTTP conformance tests to Vapor 5

Start at HTTPKeepAliveHandler.channelRead in the NIOHTTPServer module, where request heads and response .end events update connection state. Reproduce the behavior with the provided nc command, then verify HTTP/1.1 Connection: close and HTTP/1.0 without keep-alive close promptly and include Connection: close in the response.