Migrate from device_token to messaging_tokens

[jameswald]

The device_token field is now considered legacy:

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Response {
    pub request_id: String,
    pub device_token: Option<String>,

    #[serde(rename = "v")]
    pub version: String,
    #[serde(flatten)]
    pub body: ResponseBody,
}

This field and everywhere it propagates to needs to be migrated to messaging_tokens + platform. Example from other pairing clients:

/// Modern tokens including APNs and FCM
pub messaging_tokens: Option<MessagingTokens>,
/// Device platform such as iOS or Android
pub platform: Option<PushDevicePlatform>,
/// Legacy token field, use messaging_tokens with new apps
pub device_token: Option<String>,