python Expr __eq__ should check type_

[acl33]

Expr's __eq__ method is inherited from dataclass, which checks only fields/annotations declared in the instance's class, not fields/annotations inherited from superclasses. This means that type_ (declared in Expr) is not checked for any of the concrete subclasses. Hence, for example:

Const(3) == Const(3.0)

returns True.

We should require type_ to be equal for the Expr to be equal. (Since type_ may be "None" to indicate the type has not yet been computed by type propagation, we should probably add a method equals_modulo_none_type or similar.)

Note that this would happen as a side-effect of replacing KRecord with dataclass, which will automatically check inherited fields like type_. However it seems likely that most of the work here will be in fixing tests/etc. to work with this stricter definition of equality.