Using basic_new_heap for assigning elements of symbolic list

[anutosh491]

This PR adds an example to address the first TODO as pointed out here (#2450 (comment))

We are trying to replicate this code snippet essentially

from lpython import S
from sympy import Symbol, pi

def mmrv(r: Out[list[S]]) -> None:
    x: S = pi
    l1: list[S]
    l1 = [x]
    print(l1[0])
    r = l1

def test_mrv2():
    ans: list[S]
    temp: list[S]
    mmrv(ans)
    temp = ans
    print(temp[0])

test_mrv2()

[anutosh491]

Also talking about the note which added to the mentioned comment
Note: in LPython, list assignment r = l1 is always a deep copy (unlike in CPython where it is just a refcount increase), so we should initialize r first using basic_new_heap and then use basic_assign to assign the elements. That can be done later.

I see that this is correct and works without flaws, hence for now the line r = l1 can be replicated using r = l1 itself but in future we might prefer the approach pointed above.

[certik]

I think that this looks good.

[certik]

Is this ready to be merged?

[anutosh491]

Is this ready to be merged?

I think it is ready !

[certik]

The CI failure is due to #2455.