Accept any EventLoops in `.delegate(on:)`, not just ones from AHC's own ELG

The badly named but highly useful .delegate(on:) specifies two things:

1. Which EventLoop the returned futures are bound to
2. Which EventLoop the delegate callouts happen on.

Crucially it does not specify on what EventLoop the underlying Channels are running on. Yes, as an optimisation if possible & sensible (i.e. the connection pool doesn't already have a valid connection) we try to create new Channels on the same EventLoop but that's neither guaranteed nor required.

Expected behaviour

If I pass a random EventLoop to AHC's eventLoop: .delegate(on: myRandomEL) then I would expect this to work, even if AHC itself is using an EventLoopGroup that doesn't contain my EventLoop for its Channels.

Actual behaviour

AHC crashes and tells me that I can only use EventLoops from AHC's EventLoopGroup at runtime. That's bad an unnecessary.

Comienza en el punto de entrada .delegate(on:) y sigue la validación en tiempo de ejecución que restringe el EventLoop proporcionado al propio EventLoopGroup de AHC. Añade cobertura usando un EventLoop de un grupo separado y verifica después que la delegación funciona sin un crash, mientras los Channels subyacentes siguen estando gobernados por AHC.