Make default tidy3d dir configurable via environment variables

[yaugenst]

I am trying to run tidy3d on serverless containers (e.g. Google Cloud Run). These containers have read-only file systems, with only /tmp/ being writable. It would be nice if tidy3d's base/config directory could be configured via an environment variable such as TIDY3D_DIR.

Going a bit further, do you think it would be a good idea for tidy3d to adopt the XDG base directory specification, which would mean putting tidy3d's configuration in $HOME/.config/tidy3d/ by default? Resolving config directory via some precedence rules would also be cool, but probably overkill (see, e.g., how conda does it).

[tylerflex]

closing this as seems fixed by #1132