feat: add optional update_schedule method for ScheduleSource

[danfimov]

Added optional update_schedule method for ScheduleSource.

This method will be simpler to use than delete and then recreate.

[Copilot]

Pull Request Overview

This PR introduces an optional update_schedule method to the ScheduleSource abstract base class, enabling schedule sources to support updating existing schedules. This enhancement provides a standardized interface for modifying scheduled tasks, similar to the existing add_schedule and delete_schedule methods.

• Added update_schedule method to ScheduleSource ABC with comprehensive documentation
• Implemented example usage in the schedule source documentation

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
taskiq/abc/schedule_source.py	Added update_schedule method to the abstract base class with NotImplementedError for sources that don't support updates
docs/examples/extending/schedule_source.py	Added example implementation of update_schedule method demonstrating its usage

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[s3rius]

Why not just call delete and create in this method? Isn't it enough? Why do we need a separate method in each result_backend?

[danfimov]

It will be easier for library user to call one method instead of two. Like in this case for example: https://github.com/orgs/taskiq-python/discussions/535

And in postgres schedule source for example I will do delete + create in one transaction to not accidentally break something in case of connection error between two operations. Without this method user should think about it in his code and can even forget about it.