fix: add idle watcher interval cleanup and resource management

[DhyaniKavya]

issue : #5768

Problem:-
The idle watcher in js/activity.js creates a setInterval that runs every second to monitor inactivity and adjust the frame rate. The interval ID is not stored, and the activity reset event listeners are attached using a handler reference that cannot be removed.
As a result:
-the interval cannot be cleared if the activity is reinitialized
-duplicate intervals could accumulate in future lifecycle scenarios
-event listeners cannot be removed during teardown
-unnecessary resource usage may occur in long sessions or development reloads
-While this does not cause immediate user-visible errors, it represents incomplete lifecycle and resource management.

Solution:-
-This PR enables proper lifecycle cleanup while preserving all existing behavior:
-stores the idle watcher interval ID
-prevents duplicate intervals from being created
-stores the reset handler for listener removal
-adds a cleanup method to remove the interval and listeners
-does not change idle detection logic or behavior

Changes Made:-
-File modified:
->js/activity.js
->store interval ID for cleanup
->prevent duplicate interval creation
->store reset handler reference
->add cleanupIdleWatcher() method for lifecycle cleanup

Testing Performed:-
-Manual Verification
-Idle throttling activates after inactivity
-Frame rate restores on activity
-Playback and interaction behavior unchanged
-No console errors observed
-Automated Testing

Jest: ✅ all tests passed
Prettier: ✅ formatting verified
ESLint: ⚠️ pre-existing repository configuration warning (no new lint errors introduced)

Impact:-
-Improves resource and lifecycle management
-Prevents duplicate idle watcher intervals
-Enables safe cleanup for future modularization and testing
-Improves maintainability and long-session efficiency
-No breaking changes

Notes:-
This change is intentionally minimal and non-breaking. The cleanup method is opt-in and does not alter current behavior. It provides proper lifecycle handling for future use cases such as testing, development reloads, or modular integration.

Happy to adjust if maintainers prefer a different approach.

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

[Ady0333]

@DhyaniKavya
One small thought, should cleanupIdleWatcher() also be called in the activity reset/stop path (for example, right before teardown)? That would ensure no intervals or listeners remain if the activity restarts or unloads.

@vanshika2720 what do you think?

[vanshika2720]

@DhyaniKavya this is duplicate of PR #5770
please close this .

[vanshika2720]

@Ady0333 checkout PR #5770 .it is duplicate.
Yes, Adding cleanupIdleWatcher() to the reset/stop path would ensure proper teardown and avoid any potential residual listeners or intervals.
It would improve lifecycle safety.

[Ady0333]

@vanshika2720
I also noticed there is another PR (#5770) that also touches the idle watcher cleanup. Since both are working around the same area in js/activity.js, do you think it would make sense to consolidate the changes to avoid overlap?

Just thinking from a maintainability point of view.

[DhyaniKavya]

@vanshika2720 sure , i am closing this PR. Forgot to close it before. Thankyou