Add NPN and PNP BJT transistor models

[jClugstor]

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  cxontributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

Adds NPN and PNP BJT transistor models based on Ebers-Moll. These models include junction capacitances for better modeling at higher frequencies, an optional substrate pin, and optionally include the Early affect. These are similar to the Modelica NPN and PNP models, but include an option for a more sophisticated linear continuation for junction capacitances. "Computer Methods for Circuit Analysis and Design" by Jiri Vlach and Kishore Singhal (https://link.springer.com/book/9780442011949) was used as a reference.

[jClugstor]

@BenChung

[jClugstor]

It should be in the library now, and I added tests.