Support to write NFC uids directly to JSON

firmware/src/nfc.rs

@@ -1,13 +1,16 @@
 // Use custom pn532 driver instead of pn532 crate
 use crate::pn532;
 
+use crate::json::{self, ToJson};
+use alloc::string::ToString;
 use const_hex::FromHex;
 use core::convert::Infallible;
 use core::fmt::{self, Debug};
 use core::str::FromStr;
 use embassy_time::{Duration, Timer};
 use embedded_hal_async::digital::Wait;
 use embedded_hal_async::i2c::I2c;
+use embedded_io_async::Write;
 use log::{debug, info, warn};
 use pn532::{Error as Pn532Error, I2CInterfaceWithIrq, Pn532, Request, SAMMode};
 
@@ -267,3 +270,12 @@ impl AsRef<[u8]> for Uid {
         }
     }
 }
+
+impl ToJson for Uid {
+    async fn to_json<W: Write>(
+        &self,
+        json: &mut json::Writer<W>,
+    ) -> Result<(), json::Error<W::Error>> {
+        json.write(self.to_string()).await
+    }
+}

firmware/src/telemetry.rs

@@ -2,7 +2,6 @@ use crate::http::Http;
 use crate::mixpanel::{self, Mixpanel};
 use crate::{article, json, nfc, user};
 use alloc::collections::VecDeque;
-use alloc::string::ToString;
 use embassy_time::{Duration, Instant};
 use embedded_io_async::Write;
 use log::{debug, info, warn};
@@ -72,10 +71,10 @@ impl Event {
                     .await?;
             }
             Event::AuthenticationFailed(uid) => {
-                object.field("uid", uid.to_string()).await?;
+                object.field("uid", uid).await?;
             }
             Event::UserAuthenticated(_user_id, uid) => {
-                object.field("uid", uid.to_string()).await?;
+                object.field("uid", uid).await?;
             }
             Event::ArticlePurchased(_user_id, article_id, amount, total_price) => {
                 object