Pool objects owned by Fiber

[AdamRamberg]

This feature should be investigated and perf tested before being merged to main.

We are currently not pooling any objects, which we might want to do. The reason why I write might, is that it make sense for components that are mounted / unmounted often, but not for components that are only mounted once. Objects that could be pooled are:

• Children
• FiberNodes
• Effects
• Signals
• Built in components
• Refs

The idea is that the virtual node that defines all of the above (via for example F.Children) in its Render call also owns the object, meaning that when it is unmounted all object that it owns are released. A pre-requisite for this is that Signals and Refs are created by Fiber (via F).