Improve type support for the python FFI bridge

[kszucs]

The current type support is partial, here is a list about the unsupported types:

unsupported_types = [
     pa.timestamp("us"),
     pa.timestamp("us", tz="UTC"),
     pa.timestamp("us", tz="Europe/Paris"),
     pa.duration("s"),
     pa.decimal128(19, 4),
     pa.decimal256(76, 38),
     pa.binary(10),
     pa.list_(pa.int32(), 2),
     pa.map_(pa.string(), pa.int32()),
     pa.union(
         [pa.field("a", pa.binary(10)), pa.field("b", pa.string())],
         mode=pa.lib.UnionMode_DENSE,
     ),
     pa.union(
         [pa.field("a", pa.binary(10)), pa.field("b", pa.string())],
         mode=pa.lib.UnionMode_DENSE,
         type_codes=[4, 8],
     ),
     pa.union(
         [pa.field("a", pa.binary(10)), pa.field("b", pa.string())],
         mode=pa.lib.UnionMode_SPARSE,
     ),
     pa.union(
         [
             pa.field("a", pa.binary(10), nullable=False),
             pa.field("b", pa.string()),
         ],
         mode=pa.lib.UnionMode_SPARSE,
     ),
 ]

For more context see https://github.com/apache/arrow-rs/pull/439/files#r653683238

[alippai]

Timestamp and decimal128 is added here: #453

[kszucs]

Thanks @alippai for the heads-up! We can incrementally update this ticket as new types get implemented.