Replace `pos` op with `lambda x: x`

Description

Here we define the __pos__ op:

Line 403 in 2e24e67

    
           BV.__pos__ = operations.op('__pos__', (BV,), BV, calc_length=operations.basic_length_calc)

This op is really just a no-op; that is to say x == +x should always be true; thus instead of creating an op for __pos__, why do we not just replace this function with lambda x: x?

Alternatives

Leave the function as is or add a simplifier.

Additional context

It adds code bloat and wastes cycles

This is also what the Z3 backend does internally: https://z3prover.github.io/api/html/classz3py_1_1_bit_vec_ref.html#a222a5ab96b9653fccdf62318c0b75b4e

Fixed via 306