Fix: merge subscriptions from multiple #[processor] attributes

[HaoboGu]

Previously, when multiple #[processor] attributes appeared on a struct (e.g. via cfg_attr for conditional subscriptions), only the first attribute's subscribe list was honored. The macro removed all #[processor] attributes before the compiler could invoke the macro for subsequent ones, silently discarding conditional subscriptions.

Now the macro scans sibling #[processor] attributes on the struct and merges their event types into a single subscription list, enabling patterns like:

    #[processor(subscribe = [KeyboardEvent])]
    #[cfg_attr(feature = "_ble", processor(subscribe = [BleStatusChangeEvent]))]
    struct DisplayProcessor;

[github-actions]

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