Accurately apply the connect timeout in async code (#616)

Motivation

We should apply the connect timeout to the complete set of connection
attempts, rather than the request deadline. This allows users
fine-grained control over how long we attempt to connect for. This is
also the behaviour of our old-school interface.

Modifications

- Changed the connect deadline calculation for async/await to match that
  of the future-based code.
- Added a connect timeout test.

Result

Connect timeouts are properly handled

Sources/AsyncHTTPClient/AsyncAwait/HTTPClient+execute.swift

@@ -134,7 +134,7 @@ extension HTTPClient {
                     request: request,
                     requestOptions: .init(idleReadTimeout: nil),
                     logger: logger,
-                    connectionDeadline: deadline,
+                    connectionDeadline: .now() + (self.configuration.timeout.connectionCreationTimeout),
                     preferredEventLoop: eventLoop,
                     responseContinuation: continuation
                 )

Sources/AsyncHTTPClient/HTTPClient.swift

@@ -604,7 +604,7 @@ public class HTTPClient {
                 eventLoopPreference: eventLoopPreference,
                 task: task,
                 redirectHandler: redirectHandler,
-                connectionDeadline: .now() + (self.configuration.timeout.connect ?? .seconds(10)),
+                connectionDeadline: .now() + (self.configuration.timeout.connectionCreationTimeout),
                 requestOptions: .fromClientConfiguration(self.configuration),
                 delegate: delegate
             )