Siliconcompiler

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**Major:**

* Expanded and clarified the datasheet category of the schema.

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**Minor:**

* Fixed resolving paths in package sources when paths contain environmental variables.

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**Minor:**

* Fixed importing of libraries to collect package sources during import.

* Tools:

* klayout: fixed loading of schema in the presence of other modules named schema.

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**Major:**

* Added ['option', 'cache'] keypath to control the location of the cached data.
* Added support for Python 3.12

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**Major:**

* Added ['package', 'source', '<name>', 'path'] and ['package', 'source', '<name>', 'ref'] to support directly downloading of required data for a design, pdk, library, etc.

* Removed support for $SCPATH and ['option', 'scpath'] in favor of using package sources.

**Minor:**

* Tools:

* yosys: fixed handling of blackboxes during verilog reading, improved the sdc parsing to better estimate the clock for yosys-abc

* OpenROAD: fixed PDN file handling to only read files once to avoid errors from redefining the same grids.

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**Minor:**

* Removed unused ['flowgraph', '<graph>', '<step>', '<index>', 'valid'] field from schema.

* Tools:

* klayout: fixed DEF to GDS generation by ensuring the correct units are used during DEF read in and fixes the stream writing to honor OASIS if requested.

* OpenROAD: fixed handling of unidirectional layers in routing task and added tasks to support generating OpenRCX parasitic extraction decks.