Change `ServerRoute`'s `handler` type to & `HandlerDecorations`

[hhanesand]

Seems like this type definition should use & and not | if the intent is to merge properties from HandlerDecorations into the lifecycle handler.

[Marsup]

I don't think it's the same thing, the handler can either be a method or an object matching a decoration (such as here), it can't be both.