Explicit about bitwidth difference between cudf boolean and arrow boolean

[isVoid]

Currently, we map boolean type to pa.int8 because the bitwidth of cudf boolean mismatches that in arrow. However the implication of this mapping is subtle and may cause unwanted result such as:

>>> cudf.StructDtype({
    "a": np.bool_,
    "b": np.int8,
})
StructDtype({'a': dtype('int8'), 'b': dtype('int8')})

This PR changes the mapping back to pa.bool_, and use explicit type handling when we are dealing with type conversion to arrow.

[isVoid]

rerun tests

[codecov]

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[thomcom]

Can you create a test that publicly exposes this change? This kind of bit managing is easy to overlook later and a test would reveal if it is missed.

[isVoid]

rerun tests

[galipremsagar]

@gpucibot merge