Attempt to move this shared handle down the chain to skip over merged nodes.
This is for optimization only and has no semantic effects.
true if this thread reaches an unmerged node, else false if another thread modified the handle concurrently.
Progress: Lock-free, but wait-free if number of total merges is bounded.
See Implementation
Attempt to move this shared handle down the chain to skip over merged nodes.
This is for optimization only and has no semantic effects.