Print a warning when a using directive is passed inside of the REPL

[Gedochao]

Is your feature request related to a problem? Please describe.
Users get confused when Scala CLI style //> using directives are treated as regular comments in the REPL (and thus ignored).
Supporting them is a whole other can of worms, but since Scala CLI is now the official runner, it would make sense to warn users with an explanation how to use a directive when they try to paste one in the REPL.

Describe the solution you'd like
We need a warning with explanation what the user should do.
So something like:

Welcome to Scala 3.5.1 (17, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.
                                                                                                                 
scala> //> using dep com.lihaoyi::os-lib:0.10.7
[warn] using directives are not supported from inside of a REPL session. To benefit from a directive's effects, re-run the REPL using the 'scala' command and pass the directive inside of an input.                                                                            

scala> 

Describe alternatives you've considered
We could, of course, support a subset of Scala CLI directives inside of the REPL, but it's a complex discussion which is definitely outside of the scope of this issue.