Simplify autocompletion for "path" arguments and option

[pyrech]

When a Castor task expects a path to be provided to an argument or option, it could be nice to have autocompletion for it.

We could add a AsPath attribute that would automatically make the autocompletion to suggests paths. Something like:

use Castor\AsPath;
use Castor\AsTask;

#[AsTask]
function foo(#[AsPath] string $path)
{
  // ...
}