To be evaluated in 4.0

[mikearnaldi]

This comment will be updated with the ideas that we think we should evaluate for 4.0 (not currently planned)

• Equal in 4.0 (Proposal) #2855
• Kill CJS in 4.0 #2613
• Can Effect be encoded via CPS? namely can Micro become Effect?
• Can Cause<E> become Array<Fail<E> | Defect | Interrupt>?
• Can we simplify FiberRef and FiberRefs to be simple maps? we'd lose some semantics that are almost never used
• Can we have a global memoMap and auto-memoization of layers?
• Rename Tag to Context and Context to ContextMap
• Do we actually need Context, maybe Layer should be a constructor of Runtime
• Prefer type conversion and "yieldability" instead of sub-typing to minimize surprises when auto-flattening