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**Minor:**
* Search for summary image by walking backwards through the executed nodes.
* Sped up schema loading and merging by avoiding unneeded deepcopies.
* Added support to set a list in the schema with a 'set()'
* Tools:
* ghdl: added support for ['option', 'define'].
* yosys: added kogge-stone operator mapping to asic flow, removed library merging hack which is no longer needed.
* openroad: added better support for selecting global placement density, added support to control metrics and reports in tasks via ['tool', 'openroad', 'task', <task>, 'var', 'reports'].
* netgen: filter errors in stderr to ensure "Note:" are not interpreted as an error.
* klayout: allow tool to handle fill importing natively from DEF.