~ Avoid using `/dev/null` for writing DEF files (it tries to create a temp file and fail)
~ PDK now has a default value of sky130A even outside the Makefile
~ PDK_ROOT now set automatically if Volare is installed
~ Upgrade to a newer version of OpenLane 2, which in turns uses `nix-eda`
~ Format nix packages using Alejandra
~ OpenROAD scripts now read liberty files before database files (they are linked together when the database is read)
~ Update Readme to remove Colab and add banner directing people to OpenLane 2
+ Repository is now a Nix flake
~ Change all invocations of `openroad -python` to use `run_odbpy_script` for consistency
~ Change build system from ad-hoc to Nix, still producing a Docker image as a final result
~ Update KLayout scripts to use `klayout-pymod` or properly parse commandline arguments
~ `open_pdks` -> `bdc9412` to match OpenLane 2
- Remove local installer; `nix run .` will run OpenLane natively
