docs(example): collaboration state async/busy update

examples/validation/core/25_state_update.py

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+import time
+import asyncio
+from trame.app import get_server
+from trame.widgets import vuetify, html
+from trame.ui.vuetify import SinglePageLayout
+
+# -----------------------------------------------------------------------------
+# Trame app
+# -----------------------------------------------------------------------------
+
+server = get_server()
+state = server.state
+
+# -----------------------------------------------------------------------------
+# State setup
+# -----------------------------------------------------------------------------
+
+state.a = 1
+state.b = 0
+state.c = 1
+state.d = 0
+
+
+@state.change("a")
+async def change_a(a, c, **kwargs):
+    print(f"(a) server state {a=} {c=}")
+    await asyncio.sleep(2)  # async 2s wait
+    with state:
+        state.b = a * 2
+
+
+@state.change("c")
+def change_c(a, c, **kwargs):
+    print(f"(c) server state {a=} {c=}")
+    time.sleep(2)  # busy 2s wait
+    state.d = c * 2
+
+
+# -----------------------------------------------------------------------------
+# UI setup
+# -----------------------------------------------------------------------------
+
+with SinglePageLayout(server) as layout:
+    with layout.toolbar:
+        vuetify.VSpacer()
+        vuetify.VSlider(
+            label="a",
+            value=("get('a')",),
+            hide_details=True,
+            dense=True,
+            disabled=True,
+        )
+        vuetify.VSlider(
+            label="c",
+            value=("get('c')",),
+            hide_details=True,
+            dense=True,
+            disabled=True,
+        )
+
+    with layout.content:
+        with vuetify.VContainer(fluid=True):
+            html.Div("(Async) a={{a}} b={{b}} | (Busy) c={{c}} d={{d}}")
+            vuetify.VSlider(v_model=("a", 0), label="Async server handling (a)")
+            vuetify.VSlider(v_model=("c", 0), label="Busy server handling (c)")
+
+# -----------------------------------------------------------------------------
+# start server
+# -----------------------------------------------------------------------------
+
+if __name__ == "__main__":
+    server.start()