Properly output class signature for core-exts with generic parameters

[postmodern]

Describe the bug

When generating RBS type signatures for core-ext classes, sord --rbs outputs them as regular classes. They need to be outputted with generic parameters for rbs/steep to properly validate them:

To Reproduce

class Array
  def my_ext
    # ...
  end
end

$ sord --rbs defs.rbs
$ cat defs.rbs

Expected behavior

class Array[unchecked out T]
  def my_ext: () ...
end

Actual behavior

class Array
  def my_ext: () ...
end

Additional information

• sord (5.0.0)
• rbs (2.7.0)
• steep (1.2.1)