feat: transitions component for slick UI's

[maartenbreddels]

Based on Vue's transitions

TODO

• add example to pycafe + CI curl test (draft is already at https://py.cafe/solara/transitions )
• add howto add transitions

[rileythai]

Do we plan to support structures like this for transitions?

for (i,data) in dataclass.property:
    Component(data=data).key(i) # iteratively generated

where Component is some Solara component that is generated from the dataclass.

Vuetify v2 docs has something similar here. My initial try to implement a parallel format with transition-group failed but I think I had it wrong.