Panic when implicitly referring method tyarg

[yhara]

Given

class A   
  def self.foo<S>(s: S)                                             
    p Pair.new(s, s)   # == Pair<S, S>.new(s, s)
  end                                                               
end                                                                 
A.foo(3)

Expected

prints pair of 3 and 3

Actual

thread 'main' panicked at 'unexpected', lib/shiika_core/src/ty/term_ty.rs:158:18

Notes

We need to fix #493 before working on this.

[yhara]

Got another error:

thread 'main' panicked at lib/shiika_core/src/ty/term_ty.rs:165:17:
assertion failed: !typaram_ref.as_class