Add specific event helpers for `.on(EventName, handler)`

**Motivation**
Today, any struct that needs to handle events declares an `EventManager` attribute and a generic `.on()` method that simply delegates to the event manager’s registration function. However, this generic approach requires passing the event name as a first argument every time, which can be cumbersome and less ergonomic for users.

**Expectation**
The purpose of this task is to define a macro that uses the event enum to automatically:
- declares the public event enum along with its documentation
- generates a generic `.on()` method for the associated class
- generates specific alias methods like `.on_eventname(...)` for each event variant, avoiding the need to explicitly pass the event each time
- updates all examples and code samples to use the convenience alias methods rather than the generic version

**API change:**
There is no breaking change for library users, since the generic `.on()` method remains available for advanced use cases. However, examples and documentation should be updated to prefer the new convenience methods.