API: use `__new__` in `.create` to remove `__init__` totally

[Zeroto521]

Is your feature request related to a problem? Please describe.

__init__ method is not used in PySCIPOpt due to the SCIP pointer.
So create comes out to instead of __init__.
And it could still see __init__ in .create.

The chain to generate an instance via __init__.

1. Run __new__ and return a empty instance
2. Run __init__ and return this instance.

Describe the solution you'd like

use __new__ to generate a instance. It could avoid running any code in __init__.
And a little speed up via skipping the checking.

cdef class Solution:

    def __init__(self):
        raise ValueError

    @staticmethod
    cdef create(SCIP* scip, SCIP_SOL* sol):
        if scip == NULL:
            raise Warning("cannot create Solution with SCIP* == NULL")

        cdef Solution res = Solution.__new__(Solution)
        res.sol = sol
        res.scip = scip
        return res

use __init__ to generate a instance

cdef class Solution:

    def __init__(self, raise_error = False):
        if not raise_error:
            raise ValueError

    @staticmethod
    cdef create(SCIP* scip, SCIP_SOL* scip_sol):
        if scip == NULL:
            raise Warning("cannot create Solution with SCIP* == NULL")
        sol = Solution(True)
        sol.sol = scip_sol
        sol.scip = scip
        return sol