Small improvments for Mul._eval_is_real/imaginary

1. removed fuzzy_not import (it's redundant)
2. slight formatting changes
3. add an early exit if t is not a complex number
4. renamed: is_zero -> zero (like the real variable)
5. simplify "if real and is_zero is False" branch of _eval_is_real
Make Mul._eval_is_hermitian/antihermitian like Mul._eval_is_real/imaginary
Change is_integer/positive/real to _evals_is_* helpers