Some pyarrow assertions are broken in unit tests

A recent `pyarrow` release appears to have broken a few unit tests that compare the Arrow column values as follows:
```py
assert list(col) == [1, 2, 3]
```

Such conversion results in a list containing `pyarrow` scalars, causing the assertion to fail. Columns should thus be converted to Python lists with a dedicated method:
```py
col.to_pylist()
```