Add jobs argument to inform CACE about number of jobs needed

[mole99]

This PR adds the jobs argument to inform CACE about number of jobs needed to run a certain tool. This is necessary to prevent too many parameters being spawned that require more hardware threads than are available.
The jobs argument is implemented for the ngspice and klayout_drc tool.

Two other arguments, drc_script_path and spiceinit_path were implemented.

• ngspice tool:
  • Add jobs argument
  • Add spiceinit_path argument
  • By default copy the PDK spiceinit to the simulation directory
• klayout_drc tool:
  • Add jobs argument
  • Add drc_script_path argument
• Reserved variables:
  • Add CACE{jobs}
  • Add CACE{root}
• Issue a warning when a conditions has the same name as a reserved variable

[areda0]

nice additions, @mole99.

• note that the default PDK spice initialization file could be named spinit, not just spiceinit. This is the case in my volare sky130A PDK.

[mole99]

Thanks @areda0. You're right, I've updated the PDK to include a spiceinit file, but it won't be included until after the next PDK version is released. So I should probably reduce the error to a warning.