Smol writer to create a python lib directly from a nix string.
The resulting library can be consumed by the writePython3 writer.
Change-Id: Id3d793564d230b38a08f65140bda4287285e1a72
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2310
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
