Why anyio?

aiokpl is a library, not an application. Library users in the trio ecosystem cannot adopt an asyncio-only library. anyio is the standard portability layer between the two runtimes, so we depend on it and write every public stage so it works on either backend.

Practical consequences:

• Locks, events, sleeps, task groups, cancel scopes are all the anyio ones, not asyncio's.
• Every component that needs a background task (ShardMap refresh, Reducer deadline timer, Limiter drain loop) owns or receives an anyio.abc.TaskGroup.
• The test suite parametrizes anyio_backend across ["asyncio", "trio"] so each async test runs once per backend.