Run type checker for interactions without unrelated defs

[soutaro]

Type checking of a def in Steep is independent of other defs. We can just stop type checking for other defs for faster response on hover or completions.

class Foo
  def foo
    1+"     # Assume user triggers completion/hover here. 🈁
  end

  def bar
    2+3     # The type checking of this method is not used at all for the completion/hover above.
  end

  def baz
    :xyz    # We can delete these defs. 🔪 
  end
end

The test on my computer resulted in 4 times speedup of completion, from 2 seconds to 0.5 seconds. This is a huge performance improvement that 2 seconds is clearly too slow, but 0.5 seconds would be acceptable.