feat(atoms)!: remove createdAt timestamp tracking

[bowheart]

Description

Zedux core has never needed to track timestamps when nodes are created. It's always been possible for plugins to implement this and will be much easier with the new plugin system in Zedux v2.

Since this functionality is so rarely useful, it isn't worth the constant overhead, especially in prod. We'll make sure plugins can implement this. I'll also probably implement it as part of the official Zedux dev tools.

Breaking Changes

ecosystem._idGenerator.now is gone as well as the createdAt property on all atom instances and graph edges. Instead, a plugin can listen to:

• (v1) edgeCreated, evaluationFinished, and statusChanged plugin actions
• (v2) edge (which we're possibly renaming to link), runStart, and cycle ecosystem events.

and either track creation time in a separate WeakMap/similar or (not recommended) by mutating the node or edge itself.