Optimize beat reloads for far-future clocked tasks

[diaxoaine]

Description

ClockedSchedule is often used for dynamically created one-off tasks. In high-load apps, these schedules may be created very frequently, which can lead to frequent PeriodicTasks updates and cause beat to reload from the database more often than necessary, potentially as often as every 5 seconds.

This PR avoids unnecessary PeriodicTasks change updates for newly created clocked schedules/tasks that are scheduled far enough in the future.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.95%. Comparing base (89f4062) to head (f1cd98e).
⚠️ Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1041      +/-   ##
==========================================
+ Coverage   87.68%   87.95%   +0.27%     
==========================================
  Files          32       32              
  Lines        1015     1038      +23     
  Branches       81       85       +4     
==========================================
+ Hits          890      913      +23     
  Misses        107      107              
  Partials       18       18              

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[Copilot]

Pull request overview

This PR reduces unnecessary PeriodicTasks “last_change” updates (and thus DatabaseScheduler reloads) when creating new clocked schedules/tasks that are sufficiently far in the future, relying on the scheduler’s periodic full sync instead.

Changes:

• Add sync-deadline helpers (next_schedule_sync_at/by) and expose scheduler sync interval constants via utils.
• Skip PeriodicTasks.update_changed() on creation of far-future ClockedSchedule rows and far-future created PeriodicTask rows with a clocked schedule.
• Add unit tests covering in-window vs out-of-window change tracking, including configured beat_max_loop_interval.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
t/unit/test_schedulers.py	Adds tests validating when clocked creations/updates should (or should not) bump PeriodicTasks.last_change().
django_celery_beat/utils.py	Centralizes scheduler interval constants and adds helpers to compute next sync timing/deadline.
django_celery_beat/signals.py	Replaces ClockedSchedule post-save handler with a conditional version that may skip forced reloads.
django_celery_beat/schedulers.py	Uses the new helper for computing the next full-sync cutoff for excluding far-future clocked tasks.
django_celery_beat/models.py	Passes a created flag into PeriodicTasks.changed() and conditionally skips change tracking for far-future created clocked tasks.

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