Write IPC cannot write to a buffer

[pstalcup]

Polars::DataFrame#write_ipc currently only takes a string or string like as its first argument, but I would like to be able to serialize IPC to a buffer (so I can serve it through Rails directly instead of writing it to disk and then serving)

The python API supports writing to a buffer

[ankane]

Hi @pstalcup, thanks for reporting! Added in the commit above.