Use in-memory formats and dataframes as external sources in python

[amaralvieira]

Taking some inspiration from duckdb, while using python it would be quite helpful to simply reference an existing pandas dataframe/arrow table in the SELECT clause for external source.

Apart from potential efficiency gains in reducing I/O, this would greatly improve the interoperability with other python frameworks. It would definitely reduce the boilerplate code and dependency on further libraries to convert a dataframe to an hyper file.