Supporting JIT compilations for python classes .

We can firstly introduce a subset of Python.

Should look in this way:
```python
@jit
class S(Generic[T]):
    a : np.int64 # julia type Int64
    b : int # python integer
    c : Vec[T] # julia type Vector{T}
    # Vec could be given as an attached module of restrain-jit
    d : Vec[S[T]] # allow recursive definitions
``` 

```