Implement Series.get_chunks

[stinodego]

Problem description

Required for #5662

We need to be able to iterate over the chunks of a Series on the Python side. Example of desired functionality:

s1 = pl.Series([1,2])
s2 = pl.Series([3,4])

s = pl.concat([s1, s2], rechunk=False)
s.num_chunks()  # returns 2

for c in s.get_chunks():  # iterate over chunks
    print(c)  # prints `s1` then `s2`

# shape: (2,)
# Series: '' [i64]
# [
#         1
#         2
# ]
# shape: (2,)
# Series: '' [i64]
# [
#         3
#         4
# ]

Series.get_chunks should return an Iterable[Series]

Actually we'd want the same functionality for iterating over de chunks of a DataFrame, but we can probably infer this from the Series chunks.