fix[codegen]: fix double eval in dynarray append/pop

[charles-cooper]

append/pop does not have an eval once fence for the cases where it is in memory. add a fence.

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[cyberthirst]

d:DynArray[DynArray[uint256,1],1]

@external
def foo() -> DynArray[uint256, 2]:
    self.d = [[0]]
    x:DynArray[uint256, 2] = [0,0]
    self.d[x.pop()] = [1]
    return x

now crashes with AssertionError: non-unique symbols {'pop_dynarray4'}