Fixes #19006

• Added unit test TypeCheckSuite::check-expressions.test::testReverseBinaryOperator4
• Added fixture tuple-typeshed.pyi that duplicates the tuple definition from typeshed.

This patch drops the is_subtype(right_type, left_type) check in favor of the weaker covers_at_runtime(right_type, left_type).

Open Issues

• Some tests were still failing because isinstance(left_type, Instance) fails when left_type is tuple[()]. As a workaround, I changed the unconditional check

  and isinstance(left_type, Instance)
  and isinstance(right_type, Instance)
  and not (
      left_type.type.alt_promote is not None
      and left_type.type.alt_promote.type is right_type.type
  )
  and lookup_definer(left_type, op_name) != lookup_definer(right_type, rev_op_name)

  into the conditional check

  # Checking (A implies B) using the logically equivalent (not A or B), where
  #    A: left and right are both `Instance` objects
  #    B: right's __rop__ method is different from left's __op__ method
  not (isinstance(left_type, Instance) and isinstance(right_type, Instance))
  or (
      lookup_definer(left_type, op_name) != lookup_definer(right_type, rev_op_name)
      and (
          left_type.type.alt_promote is None
          or left_type.type.alt_promote.type is not right_type.type
      )
  )

  But I am not sure this is the correct thing to do.

• (FIXED) I get different results when running tests versus checking a file manually:

  $ pytest mypy/test/testcheck.py::TypeCheckSuite::check-expressions.test
  
  Expected:
  Actual:
  main:15: error: Expression is of type "Tuple[int, ...]", not "Size" (diff)
  main:16: error: Expression is of type "Tuple[int, ...]", not "Size" (diff)
  

  versus

  $ mypy example.py
  example.py:4: error: Signature of "__add__" incompatible with supertype "tuple"  [override]
  example.py:4: note:      Superclass:
  example.py:4: note:          @overload
  example.py:4: note:          def __add__(self, tuple[int, ...], /) -> tuple[int, ...]
  example.py:4: note:          @overload
  example.py:4: note:          def [_T] __add__(self, tuple[_T, ...], /) -> tuple[int | _T, ...]
  example.py:4: note:      Subclass:
  example.py:4: note:          def __add__(self, tuple[int, ...], /) -> Size
  example.py:14: error: Expression is of type "tuple[int, ...]", not "Size"  [assert-type]
  example.py:15: error: Expression is of type "tuple[int, ...]", not "Size"  [assert-type]
  example.py:16: error: Expression is of type "tuple[int, ...]", not "Size"  [assert-type]
  example.py:18: error: Expression is of type "tuple[int, ...]", not "Size"  [assert-type]
  Found 5 errors in 1 file (checked 1 source file)