Warn if duplicate CommandHandlers are registred for same type.

[NickJosevski]

In EventfulHandlers
CommandHandlers : Map<string, EventfulCommandHandler<CommandResult<'TBaseEvent, 'TMetadata>, 'TCommandContext, 'TMetadata>>

AddCommandHandler will quietly replace the any existing command handler with an subsequent one with the same name. A warning would be sufficient then actions can be taken to create different naming for those commands.

In contrast AddEventHandler does cater for multiple using Map.insertWith List.append evtName [handler]

[adbrowne]

Sounds good. Will look at this shortly. I think your first suggestion of a warning is probably the best - it's feasable to support multiple handlers for the one command but might lead to partial command failures.

[NickJosevski]

No rush, Dave or I might get to it before you. Yea we thought multiple commands needed much more thought.

Pattern for supporting multiple commands is reasonably neat