Add PR example demo for Generic[TModel] support

Author: rodrigo.nogueira

pr_example_demo.py

@@ -0,0 +1,51 @@
+"""
+Example from PR description - demonstrating Generic[TModel] support
+"""
+
+import sys
+
+sys.path.insert(0, ".")
+
+from statemachine import StateMachine, State
+
+
+class MyModel:
+    def __init__(self) -> None:
+        self.state: str | None = None
+        self.custom_field: str = "test"
+
+
+class MyMachine(StateMachine[MyModel]):
+    initial = State("Initial", initial=True)
+    processing = State("Processing")
+    done = State("Done", final=True)
+
+    go = initial.to(processing)
+    finish = processing.to(done)
+
+
+# Create instance
+sm = MyMachine(model=MyModel())
+
+# This is what the PR description shows
+print(f"✅ Created state machine: {sm.current_state}")
+print(f"✅ Model custom_field: {sm.model.custom_field}")
+
+# Demonstrate it works
+assert sm.model.custom_field == "test"
+assert sm.current_state == sm.initial
+
+sm.send("go")
+assert sm.current_state == sm.processing
+
+sm.model.custom_field = "modified"
+assert sm.model.custom_field == "modified"
+
+sm.send("finish")
+assert sm.current_state == sm.done
+
+
+print(f"✅ Final state: {sm.current_state}")
+print(f"✅ Modified custom_field: {sm.model.custom_field}")
+
+print("\n✅ PR description example works perfectly!")