Allow inheritance from standard cells

[sebastian-goeldi]

Move the code creating the KCell from __call__ for _kcell.

This will allow to make inheritance.

E.g.

```Create a post-processed waveguide```
import kfactory as kf

class TestBendEuler(kf.cells.euler.BendEuler):  # type: ignore[unused-ignore, misc]
    def __init__(self) -> None:
        super().__init__(kf.kcl)

    @kf.cell  # type: ignore[misc, unused-ignore]
    def __call__(self, width: float) -> kf.KCell:  # type: ignore[override, unused-ignore]
        c = self._kcell(
            width=width,
            radius=30,
            layer=LAYER.WG,
            enclosure=wg_enc,
            angle=90,
            resolution=150,
        )
        c.info.creation_time = "2023-02-12Z23:00:00"

        return c

# could also use bend_euler = TestBendEuler()
bend = TestBendEuler()(width=1)

[sebastian-goeldi]

@joamatab is this what you roughly wanted?

[joamatab]

not really, this seems overly complicated

i prefer functions over classes, as they are easier to read and to write

[sebastian-goeldi]

You have to choose, either make it inheritable as a class or use no decorator.

With this you now have three choices:

• The above
• my_kcell.dup() (needs name change to avoid collision, i.e. doesn't change the cached KCell)
• use e.g. kf.cells.straight.straight._kcell(...) to get the uncached version directly and wrap that in a @cell decorator to cache (this will not set all settings though, only the ones passed to the new function with @cell)

I can't give you something to inject a post_process into an existing function. At that point, just unlock the cell and modify it, it's the same as if you were grabbing kwargs from the footprint of the function.

[joamatab]

then, l prefer keeping the cell decorator as it is and then passing an explicit post_process function

gdsfactory/gdsfactory#2524