HTTP1ConnectionsProvider shutdown isn't quite sound

[weissi]

This test:

        XCTAssertNoThrow(try HTTP1ConnectionProvider(key: .init(.init(url: "http://some.test")),
                                                     eventLoop: self.eventLoop,
                                                     configuration: .init(),
                                                     pool: .init(configuration: .init(),
                                                                 backgroundActivityLogger: HTTPClient.loggingDisabled),
                                                     backgroundActivityLogger: HTTPClient.loggingDisabled)
                            .close().wait())

hangs forever (because there's 1 pending connection) which isn't right.

The connection provider (is probably wrongly) expecting that acquire will come along and decrease pending. I'd argue it a) shouldn't wait for acquire to come along b) acquire cannot actually do that right now because acquire only decreases pending IF we're .active.

That's a real race that can happen in real usage I believe.