add opt-in asyncio task integration

docs/plugin-api-additions/async.md

@@ -0,0 +1,30 @@
+# Optional Python asyncio integration
+
+`run_async(coroutine, context=None, interval=10)` returns an AsyncTask with
+`done()`, `cancel()` and `result()`. Each invocation owns a separate event loop
+pumped by an existing main-loop timer. A ready stop callback ensures selector
+polling never blocks the UI. The captured context is restored after every pump;
+a closed context cancels the work. No process-wide event-loop policy is changed.
+
+Existing synchronous scripts are unaffected. Use `asyncio.get_running_loop()`
+inside the coroutine. Child tasks use the same loop/context and are cancelled
+when the main coroutine finishes or the script unloads. Cancellation cleanup is
+bounded; tasks must not suppress cancellation indefinitely. Cleanup uses the
+captured context while it remains open; after it closes, cancellation cleanup uses
+the current valid context. Use explicit Context methods for context-specific
+output in finally blocks, and do not issue context-dependent commands there. This provides normal
+asyncio sockets/timers, not Windows subprocess support or a new HTTP library.
+Asyncio hostname resolution can use its executor; use a resolver appropriate to
+your library if you require no worker threads. Blocking work inside a coroutine
+still blocks the client and must be avoided.
+
+```python
+import asyncio
+import zoitechat
+
+async def later():
+    await asyncio.sleep(1)
+    zoitechat.prnt('Still in the context where this task was started')
+
+task = zoitechat.run_async(later())
+```