Support //> using exclude in .sc script files

[Gedochao]

Scala CLI version
1.5.4 and 4ab3227

Is your feature request related to a problem? Please describe.
Currently the //> using exclude directive is only allowed in project.scala.

Describe the solution you'd like
When using a .sc script (which may include some sources via //> using file), I may not have a project.scala in my project, so I'd just like to declare it in my script.
The directive should still only be allowed to exist in a single source file, similar to //> using file, to avoid parsing insanity.

Describe alternatives you've considered
Expect a project.scala always be included via //> using file when //> using exclude is necessary in a script setup.