refactor(db-scheduler): optimize all_as_schedule query

[alirafiei75]

Summary

This PR optimizes the all_as_schedule function to improve performance by filtering unnecessary tasks from the database query.

Changes

• Exclude clocked tasks not due within 5 minutes.
• Exclude crontab tasks outside the relevant hour range.

fixes #675
fixes #786

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.40%. Comparing base (17d87f4) to head (0205cdf).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #835      +/-   ##
==========================================
+ Coverage   87.20%   87.40%   +0.20%     
==========================================
  Files          32       32              
  Lines         938      953      +15     
  Branches       76       76              
==========================================
+ Hits          818      833      +15     
  Misses        102      102              
  Partials       18       18              

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[alirafiei75]

This is cpu usage of our celery-beat server. We depend highly on cronjobs and clockjobs and as you see, optimizing the scheduler query, led to reduction in cpu usage considerably (see 11:53 in the picture)