* `Yosys.JsonHeader`, `Yosys.*Synthesis`
  * **Internal**:
    * Steps are no longer `TclStep`s: rewritten in Python and now use `libyosys`. While there are no functional changes, this enhances the codebase's consistency and helps avoid tokenization-related security issues.

* `Yosys.*Synthesis`
  * ABC scripts used now created dynamically and dumped as a `.abc` file into the step directory.

* Updated `nix-eda`
  * `yosys` -> `0.44` (+ `-y` patch)
  * `klayout` -> `0.29.4`
  * OpenROAD now used with new `withPythonPackages` features to use Python packages specifically for the OpenROAD environment

* `OpenROAD.*`
  * Added `log_cmd` from OpenROAD-flow-scripts -- neat idea for consistency
  * **Internal**: Steps now sensitive to `_OPENROAD_GUI` environment variable -- coupled with `--only`, it runs a step in OpenROAD then doesn't quit so you may inspect the result.
    * This is not part of the OpenLane stable API and may be broken at any moment.

* `OpenROAD.CutRows`
  * Rows that generate less than a specified number of sites are now removed to help with PDN generation (default: 25)

* Created `OpenROAD.HierarchicalMacroPlacer`
  * Based on OpenROAD `mpl2`-- a macro placer that uses hierarchy information from the RTL to generate a macro placement automatically
  * Used for macros for which a manual placement has not been provided

* Created `OpenROAD.UnplaceAll`
  * Removes placement status of all instances.

* `Yosys.Synthesis`
  * `SYNTH_NO_FLAT` replaced with `SYNTH_HIERARCHY_MODE` with three options: `flatten` (previously `false`), `deferred_flatten` (previously `true`) and `keep` (new value). When set to `keep`, the netlist generated is hierarchical.

## Flows
* Classic
  * Added `OpenROAD.HierarchicalMacroPlacer` after `Odb.ManualMacroPlacement`
  * Moved pin placement flow before macro placement as `mpl2` requires pin placement information
  * Added `OpenROAD.UnplaceAll` after pin placement so rows can be cut for macros without worries about already-placed instances

## Tool Updates
* `openroad` -> `49a497a`
* Enhanced overlay for `or-tools` to fix a bug where trying to build OpenROAD from a git repo (using nix develop .#openroad) would Cmake always fail after the first `cmake ..`