feat: support custom Python events with optional cancellation

[wu-vincent]

Summary

• Add PyEvent trampoline class (event.h) enabling Python subclasses of Event to work through pybind11 — previously custom events were not possible in the Python API
• Move Cancellable to a pure Python mixin so custom events can opt into cancellation via class MyEvent(Event, Cancellable) multiple inheritance
• Remove deprecated cancelled property (replaced by is_cancelled in a prior release)
• Fix event name resolution — built-in events use the short class name, custom plugin events use fully qualified module.qualname to avoid collisions
• Fix EventHandler dispatch — use virtual isCancelled() on Event so cancellation state is read correctly for both C++ and Python events
• Add unit tests (tests/test_event.py) and runtime integration tests (tests/endstone_test/.../test_custom_event.py)

Example

from endstone.event import Cancellable, Event, EventPriority, event_handler
from endstone.plugin import Plugin


# Define a simple custom event
class MyCustomEvent(Event):
    def __init__(self, message: str):
        super().__init__()
        self.message = message


# Define a cancellable custom event
class MyAnnouncement(Event, Cancellable):
    def __init__(self, text: str):
        super().__init__()
        self.text = text


class MyPlugin(Plugin):
    def on_enable(self):
        self.register_events(self)

    # Listen for the custom event
    @event_handler
    def on_custom(self, event: MyCustomEvent):
        self.logger.info(f"Received: {event.message}")

    # Listen with priority, skip if cancelled
    @event_handler(priority=EventPriority.HIGH, ignore_cancelled=True)
    def on_announcement(self, event: MyAnnouncement):
        self.server.broadcast_message(event.text)

    def some_method(self):
        # Fire the events
        self.server.plugin_manager.call_event(MyCustomEvent("hello"))

        announcement = MyAnnouncement("Server restarting soon!")
        self.server.plugin_manager.call_event(announcement)
        if not announcement.is_cancelled:
            # proceed with default behavior
            ...

Design

• C++ events continue to use Cancellable<T> template + ICancellable pybind11 binding
• Python custom events use PyEvent as the trampoline, which implements ICancellable by reading/writing the _cancelled attribute on the Python object — consistent with the Python Cancellable mixin
• PyEvent::isCancellable() checks at runtime whether the Python class inherits from the Python Cancellable mixin
• Event now has a private virtual isCancelled() so EventHandler dispatches correctly for both C++ (reads cancelled_ field) and Python events (reads Python attribute) via vtable

Test plan

• pytest tests/test_event.py — unit tests for custom event name, async flag, cancellation, un-cancellation, and async+cancellable
• Runtime integration tests (test_custom_event.py) — fire/handle cycle through plugin manager, cancellation priority semantics
• Existing event tests still pass
• C++ tests (ctest) unaffected

🤖 Generated with Claude Code