feat(context): Add contexts subclasses feature

[CCXLV]

This PR adds a Context class to implement Dependency Injection for worker tasks.

Key Changes

• task_with_context: A new decorator that automatically injects the context as the first argument. Developers no longer need to pass the context manually when calling the task function.

• thread_storage: Uses threading.local within the Context class to store long-lived resources like database engines, ensuring thread isolation.

• metadata: Provides access to task-specific execution data such as task_id, retry_count, max_retries, and enqueued_at.

Example

@fluxqueue.task_with_context()
def my_task(ctx: Context, param: str):
    print(ctx.metadata.task_id)
   
# ctx is injected; only param is passed by the caller 
my_task("Hello")