pos*: point_of_sale, pos_loyalty, pos_hr, pos_online_payment, pos_stock,
l10n_in_pos, l10n_id_pos

Refactor the customer display communication to make it more efficient,
decouple the terminal and display sides, and avoid unnecessary requests
when no display is connected.

- Replace the effect on `pos_service` with targeted listeners on order-related events.
- Split `customerDisplayService` into two OWL plugins: `CustomerDisplayTerminalPlugin` for the PoS terminal and `CustomerDisplayPlugin` for the customer display.
- Centralize payload generation through `GeneratePrinterData` and remove the deprecated `CustomerDisplayPosAdapter`.
- Replace `device_uuid` with a `device_identifier` generated by `DeviceIdentifierSequence`.
- Use a registration route to track connected customer displays: displays announce themselves with `ADD` and `REMOVE`, while terminals use `PING` to discover displays after startup or reload.
- Skip payload generation and requests when no customer display is connected.
- Refactor customer display tests to exercise the real application flow and assert against system-generated payloads.

```mermaid
flowchart LR
    POS([PosStore])
    UI([Customer display UI])

    subgraph Terminal["CustomerDisplayTerminalPlugin — app/plugins"]
        direction TB
        initT["init({ identifier, models, scale, bus, ... })"]
        sendOrder["sendOrder(order)"]
        build["_buildDisplayPayload()"]
        send["send(payload)"]

        sendOrder --> build --> send
    end

    subgraph DisplaySide["CustomerDisplayPlugin — customer_display"]
        direction TB
        initD["init({ bus })"]
        onData["_onDataReceived()"]
        data[("data — signal")]

        onData --> data
    end

    POS -->|initCustomerDisplay| initT
    POS -->|order or screen changed| sendOrder
    UI -->|mounted| initD

    send -->|"update_customer_display — bus"| onData
    send -.->|"BroadcastChannel — only if the request fails"| onData
    data -->|render| UI
```

Task-5911881