Issue

Almost all of the methods in the LayoutTree trait either take a taffy::Node (which is an alias for slotmap::DefaultKey) as a parameter or are required to return one. But the only way to create or use a slotmap::DefaultKey is to depend on the slotmap crate and actually a have a slotmap allocated in memory!

This is not ideal considering the whole point of the LayoutTree trait is to enable alternative storage backends.

Context

The LayoutTree trait definition: https://github.com/DioxusLabs/taffy/blob/main/src/tree.rs

I'm currently trying to create a grid widget for iced using Taffy for layout. Hopefully this should be a good test case that will surface issues like this that make Taffy to integrate with.

Proposal

The LayoutTree trait should be decoupled from slotmap. Possibly by making the node id an associated type on the trait, or just standardising on u64 instead of slotmap::DefaultKey.