feat: override clone method to only allow for deep clones

[akselthomsen]

Should we override the default clone method of a connector object to only allow for deep clones following the discussion in #18 ?

As of now a connector object remains cloneable, but with the default deep=FALSE.
So far two ways of changing this has been identified:

1. Change the default value of the cloning method with:
   formals(connector$public_methods$clone)[["deep"]] <- TRUE
   Pro: Easy solution, and Rd documentation will still be correct
   Con: Confusing for experienced R6 users that the standard clone method has a different method

2. Create a custom clone method for the connector object with only deep cloning available.
   One solution could be:
   connector$set("private", ".clone", connector$public_methods$clone, TRUE)
connector$set("public", "clone", \() private$.clone(deep = TRUE), TRUE)
   Another could be to internalise the clone method and always have deep = TRUE.
   Pro: Robust, and only allows for deep clones
   Con: Cannot override the roxygen documentation, and might need us to have cloning under a new method name.

Useful references:

• https://stackoverflow.com/questions/53935619/changing-cloning-behavior-in-r6-classes
• https://github.com/r-lib/R6/blob/main/R/clone.R