Improve and generalize sized type checking

[zanellia]

As of now sized type checking is carried out in a rather case-specific fashion. At some point, the typed_record (https://github.com/zanellia/prometeo/blob/master/prometeo/cgen/code_gen_c.py#L324) and the var_dim_record (https://github.com/zanellia/prometeo/blob/master/prometeo/cgen/code_gen_c.py#L328) generated during the static analysis should be merged into a single dictionary and they should support any valid sized type e.g

n : dims = 10
A : pmat = pmat(n,n)

class ClassA():
    A : pmat = pmat(n,n)

class ClassB():
    A : pmat = pmat(n,n)
    B : ClassA = ClassA()

As of now 1) and 2) work fine, but to support 3) and more sophisticated user-defined sized types the code needs some restructuring.

In particular, if we analyze

from prometeo import *

n : dims = 10

class ClassA():
    A : pmat = pmat(n,n)

def main() -> int:
    A : pmat = pmat(n,n)
    return 0

it will result in the following typed_record:

{
    "global": {
        "n": "dims"
    },
    "global@ClassA": {
        "A": "pmat"
    },
    "global@main": {
        "A": "pmat"
    }
}

and the following var_dim_record:

{
    "global": {},
    "global@ClassA": {
        "A": [
            "n",
            "n"
        ]
    },
    "global@main": {
        "A": [
            "n",
            "n"
        ]
    }
}