Fix skips/todos on property tests

[billylanchantin]

We discovered a number of bugs while developing #1012. This issue will keep track of known bugs and our progress on them.

• [x] DataFrame.new!/2 fails often with the :decimal dtype
• [x] Can't print empty DataFrames
  • [ ] DF.new([], dtypes: %{a: :integer}) results in 0 columns instead of 1
• [ ] Can't print DataFrames in certain scenarios:
  • [x] :millisecond datetimes with high years
  • [ ] {:list, {:struct, ...}} columns
  • [ ] This panics with assertion failed: i < self.len():

     dtypes = [{"col_k", {:list, {:struct, [{"r", :category}]}}}]
     cols = [{"col_k", [[], [%{"r" => ""}]]}]
     df = DF.new(cols, dtypes: dtypes)

• [ ] Can't dump to CSV in certain scenarios
• [ ] Can't dump to IPC in certain scenarios
• [ ] Can't dump to NDJSON in certain scenarios
• [ ] Can't dump to PARQUET in certain scenarios

Feel free to edit this description with updates to the bug-list.