test(cypress): defer ResizeObserver callbacks to next frame

[pringelmann]

Summary

users_manager.cy.ts has been crashing the Electron renderer on CI repeatedly. Heap snapshots ruled out OOM (dialog mount only adds ~2 MB to JS heap). A local Cypress pre-crash video shows ResizeObserver loop completed with undelivered notifications firing several times when the edit dialog and the Manager NcSelect open.

The loop seems to come from Floating UI's autoUpdate (used by NcSelect for popper positioning): each resize triggers a position recalc, which changes layout, which triggers another resize. We already suppress this as an uncaught exception in cypress/support/e2e.ts, but suppression only helps if the renderer survives. On slower CI CPUs the loop tanks the main thread until Electron's page unresponsive watchdog kills the renderer outright. Cypress then reports a generic renderer crashed with boilerplate advice about experimentalMemoryManagement and numTestsKeptInMemory (red herring, neither helped).

This patches ResizeObserver so callbacks fire on the next animation frame, breaking the synchronous loop. Workaround in the test harness, not a real fix. The proper fix belongs upstream in @nextcloud/vue and will be filed separately.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)