State union should fail on Variable normalization conflict.

[proofit404]

class A1State(State):
    v1 = Variable(is_integer)

class A2State(State):
    v1 = Variable(is_float)

NewState = A1State & A2State

The v1 variable in the NewState would fail on assignment. It can't be integer and float at the same time.

Checks:

• conflict (error message shows between which states it happen & normalized values which are not equal)
• in composition of thee layers

[proofit404]

Superseded by #722