Cannot Create Decimal Series using Series initializer

[simbasdad]

This is a follow up to #21.

As far as I can tell, there's no way to use the Series initializer (or cast) to construct a dataframe with a Decimal datatype.

Polars::Series.new("revenue", raw_table[:revenue], dtype: :decimal)
Polars::Series.new("revenue", raw_table[:revenue], dtype: Polars::Decimal)

both obvious fail because there is not currently a decimal datatype.

Polars::Series.new("revenue", raw_table[:revenue].map { |r| BigDecimal(r, 10) } )

constructs a series, but the type is object.

Currently we only need this for testing purposes to verify that our production code will indeed work with Decimal columns after updating to 0.5.1.

[simbasdad]

Ignore this. I misread the commit that fixed #21. Thanks again.