Better PDK cells

[sebastian-goeldi]

• [x] Allow c << pdk.cell when pdk.kcl (or pdk.kcl.layout is not the same as c.kcl (or layout).
• [x] KCLayout has always a layout object with a library() is not None
• [x] Force pdk naming (necessary for library registration in order to derive library name from pdk)
• [x] Register the Library objects by pdk name
• [x] Make the library cells not defunct when the library gds is not registered to the GUI (make them static but with proper name prefix)
• [x] New pdk tests
• [x] Readd LayerEnclosures and KCellEnclosure

Other fixes:

• [x] Fix pydantic 1 artifacts (move class Config to class definition)
• [x] Fix config for proper support of pydantic-settings

@joamatab @SkandanC

[sebastian-goeldi]

Still needs some updates, but pls review already @SkandanC @joamatab