[Feature][Python] Implement EventListener to align with Java SDK

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/flink-agents/issues) and found nothing similar.

### Related PR
- #641
- #102

### Description

This feature introduces the `EventListener` interface to enable event-driven monitoring and custom logic extensions within the Flink Agent Python SDK, aligning with the existing Java SDK implementation.

#### Design Considerations

During the initial design phase, I explored two different approaches for registering event listeners:

**Option 1: Decorator-based Registration (Considered)**
I initially evaluated a Pythonic approach where a decorator registers a standalone function as a listener by storing its metadata in an internal registry.
```python
# Information stored in an internal registry
REGISTRY = []

def event_listener(func):
REGISTRY.append({
"module": func.__module__,
"qualname": func.__qualname__
})
return func

@event_listener
def my_handler(context, event):
print(f"Received: {event}")
```

*Pros:* Highly idiomatic and concise for Python developers.
*Cons:* This approach deviates significantly from the class/interface-based structure of the Java SDK, breaking API consistency across different language SDKs.

**Option 2: Class-based Interface (Final Decision)**
To maintain a unified developer experience and ensure structural alignment with the Java SDK, I decided to adopt a **class-based interface design**.

#### Proposed API Usage

The user implements the `EventListener` interface, and the framework dynamically instantiates and triggers it during the event lifecycle.

```python
from flink_agents.api.listener import EventListener
from flink_agents.api.event_context import EventContext
from flink_agents.api.events import Event

class MyCustomListener(EventListener):
def on_event_processed(self, context: EventContext, event: Event) -> None:
print(f"Event processed: {event.type} at {context.timestamp}")

# Registration via environment configuration
agents_env.get_config().set(
AgentConfigOptions.EVENT_LISTENERS,
[str(MyCustomListener)]
)
```

### Are you willing to submit a PR?

- [x] I'm willing to submit a PR!

Start with the proposed Python API modules flink_agents.api.listener, flink_agents.api.event_context, and flink_agents.api.events, then compare their intended structure with the existing Java SDK implementation. Trace how AgentConfigOptions.EVENT_LISTENERS is read and how listeners are instantiated and triggered during the event lifecycle. Done means the class-based EventListener usage shown in the issue works and remains aligned with the Java SDK.

Written by the indexing model from the issue text.