Scheduler - Appointment popup may send redundant resource load requests on every opening

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I investigated whether reusing the appointment popup instance causes redundant CustomStore.load() calls on every popup opening.

• Traced the full resource loading pipeline. Found 4 existing guards that prevent the regression
• Confirmed manual reproduction is impossible by design (scheduler blocks rendering until resources load)

Guards already in place. Test serves as a safety net if any of the guards are removed in future refactoring

[Copilot]

Pull request overview

Adds an integration test in the internal Scheduler appointment popup suite to ensure that reopening the appointment popup does not trigger redundant CustomStore.load() calls for resources, serving as a regression safety net around resource-loading guards.

Changes:

• Add a new integration test that opens/hides/reopens the appointment popup and asserts CustomStore.load() is called only once.
• Add a Resources-scope timer cleanup (jest.useRealTimers()) to avoid fake-timer leakage across tests in that block.