feat: Session Window and Reduce Streaming

[yhl25]

• A new server has been introduced specifically to execute SessionReducer operations and will listen to "/var/run/numaflow/sessionreduce.sock".

• Made Proto modifications to support streaming reduce and session reduce.

• A task manager is now included in all the reducers for better management of reduce tasks.

• The reducer interface has been updated, it now returns a channel to support partial responses and early returns. (breaking change)

• Type Messages from the reducer has been removed since the handler return type is now a channel. (breaking change)

[vigith]

let's also rethink the need of locking required in Aligned windows