Spike S5: tune auto-switch detection window and debounce on real devices

DESIGN.md sections 4.4, 10 and 11 (S5).

Engine has two values that are guesses and still need tuning:

debounceDelay = 0.4 s: how long the app waits to group device-list events (for example Bluetooth reconnect storms after wake).
autoSwitchWindow = 2 s: a default-device change within this time after a connect, pointing at the newly connected device, counts as a macOS auto-switch instead of a manual choice.

To verify, with USB, Bluetooth, AirPlay and HDMI/DisplayPort devices

The order and timing of "device list changed" and "default device changed" events on connect.
A lower-ranked device that connects and gets auto-switched by macOS is reverted (table 6.4).
A higher-ranked device that connects becomes active.
A manual choice in Control Center right after a connect is not reverted, or document that this is a known limitation.
Sleep/wake with several Bluetooth devices ends up on the highest-ranked device.
Make sure no switching loop happens.

If it fails: find a different signal, or accept occasional misclassification and document it.

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