Allow async condition predicates

[Suke0811]

Summary

• allow RateControl to await coroutine condition predicates in async modes while rejecting them in synchronous loops
• update the spin decorator/context docs and cheatsheet to document the new behaviour and show async predicate examples
• extend the test suite with async condition coverage and a guard that sync loops raise when given coroutine predicates

Testing

• pytest

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https://chatgpt.com/codex/tasks/task_e_68d43b5c1460832c8c05c82db71e4be0