Introducing "observers" to monitor special activities on the container.

[SmallHuaZi]

Hello, maintainers. Recently i’ve been studying some fascinating kernel-level design patterns in Linux and Zircon, particularly augmented RB-trees and SubtreeObserver. These mechanisms enable efficient monitoring and reactive updates for specific operations on a container.For example, in Linux, the augmented RB-tree allows us reactively update additional scheduling metadata when balance actions happened on the tree. So is it feasible to implement it as a new option in the existing container design?