Mark Priority as stable

[yuandrew]

What was changed

Removed experimental wording from Priority APIs and added a changelog entry.

Why?

Priority is no longer experimental.

Checklist

1. How was this tested:

   • Ruby syntax checks for each changed source file
   • git diff --check

2. Any docs updates needed?

   • No. YARD comments and the changelog are updated.

---

Note

Low Risk
Documentation and changelog only; no runtime or API behavior changes.

Overview
Priority is documented as stable: YARD comments no longer call the priority: option experimental on client workflow/activity APIs, schedule start-workflow actions, with-start workflow operations, and in-workflow activity/child workflow scheduling.

The unreleased changelog notes that Priority is no longer marked experimental. Behavior and APIs are unchanged—only docs and release notes.

^{Reviewed by Cursor Bugbot for commit 6eed0ba. Bugbot is set up for automated code reviews on this repo. Configure here.}