Add new schedule module

[waynemwashuma]

Objective

Refactors the project's scheduling and execution system by extracting scheduling-related modules from the ECS and app module into a new, dedicated schedule module.This separation was taken because:

• Scheduling is a distinct concern from core ECS functionality
• The scheduling system could be used independent of ECS(not in its current state)
• It follows the principle of separation of concerns
• It improves code discoverability and maintainability

Solution

The scheduling system (including schedulers, executors, and related components) was previously housed within the ECS module. This PR:

• Creates a new top-level schedule module with proper internal structure
• Moves all scheduling-related functionality to this new module

Migration Guide

This is internal and shouldn't affect most users.

Checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.