Match the cancellation guide, `Portal.cancel_actor()` contract and
duplicate-name regression comments to the actor-nursery impl: a failed
bounded cancel request escalates directly to `proc.kill()`.
Keep the older terminate-then-kill path documented separately for its
remaining legacy callers.
Review: PR #481 (goodboy)
https://github.com/goodboy/tractor/pull/481#pullrequestreview-5012942328
(this patch was generated in some part by `opencode` using `gpt-5.6-sol` (`openai`))