Add regression test for accordion rapid-click exit animation (#2674)

[mattgperry]

Summary

Adds a Cypress regression test for the accordion rapid-click scenario reported in #2674 (motion.section with an explicit `key` inside `AnimatePresence`, rapidly toggled open/closed).

Investigation

The original CodeSandbox could not be fetched (CloudFlare-blocked), so the test reconstructs the scenario from the reporter's description and screenshots:

• Multiple accordion items, each with its own `AnimatePresence`
• A keyed `motion.section` conditionally rendered inside
• `height: 0` ↔ `height: "auto"` enter/exit

The reporter observed visual glitches under rapid clicking and noted that removing the `key` from the `motion.section` resolved it.

I could not reproduce the bug against the current codebase. All three test variants pass (open mid-exit, close mid-enter, 5x rapid toggle) on both React 18 and React 19 without any code changes.

The issue was filed in May 2024, and numerous `AnimatePresence` rapid-switching / re-entry fixes have landed since — likely resolving it transitively:

• `90d8c5364` Fix AnimatePresence not removing children when exit matches current values
• `10427ae38` Fix AnimatePresence stuck when state changes too fast in mode='wait'
• `6a8d3abb9` Fix AnimatePresence re-entry: replay enter animation when exit completed
• `05842be0d` Fix AnimatePresence wrong animation direction when key re-enters during exit
• `8798d7017` Fix AnimatePresence keeping exiting children in DOM during rapid updates with dynamic variants
• `aa8b46be3` Fix duplicate exit animation processing in AnimatePresence

The test is included as a forward regression gate covering the specific keyed-child accordion pattern, so any future regression in this area would be caught immediately.

Opening as draft because no production code is changed — please confirm whether the bug is indeed considered resolved and the test should land on its own. If it should be closed without merging, that's also fine.

Fixes #2674

Test plan

• `yarn build` passes
• `yarn test` passes (776 tests)
• New Cypress spec passes on React 18
• New Cypress spec passes on React 19