chore(cable): drop dead unsafe Send/Sync, fix top-of-README table

CableQrCodeDevice's fields (NonZeroScalar, ByteArray, Option<Arc<dyn
CableKnownDeviceInfoStore>>) all auto-derive Send + Sync, so the
hand-rolled unsafe impls are dead. Verified compile-time via a
T: Send + Sync assertion in the test module; downstream consumers
(credentialsd spawns CableQrCodeDevice across tokio::spawn) keep working.

Also brings the top-of-README transport-support table in line with the
example table further down — caBLE v2 plus CTAP 2.3 hybrid.

Author: AlfioEmanueleFresta

README.md

@@ -51,7 +51,7 @@ Validating the relying party ID against the calling origin requires the [Public
 | **Bluetooth Low Energy**     | 🟢 Supported (bluez)  | 🟢 Supported (bluez)  |
 | **NFC**                      | 🟢 Supported (pcsc or libnfc) | 🟢 Supported (pcsc or libnfc) |
 | **TPM 2.0 (Platform)**       | 🟠 Planned ([#4][#4]) | 🟠 Planned ([#4][#4]) |
-| **Hybrid (QR code scan, aka caBLE v2)**         | N/A                   | 🟢 Supported          |
+| **Hybrid (QR code scan, caBLE v2 + CTAP 2.3)**  | N/A                   | 🟢 Supported          |
 
 ## Example programs
 

libwebauthn/src/transport/cable/qr_code_device.rs

@@ -231,10 +231,6 @@ impl CableQrCodeDevice {
     }
 }
 
-unsafe impl Send for CableQrCodeDevice {}
-
-unsafe impl Sync for CableQrCodeDevice {}
-
 impl Display for CableQrCodeDevice {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         write!(f, "CableQrCodeDevice")
@@ -302,6 +298,13 @@ mod tests {
     use super::*;
     use std::collections::BTreeMap;
 
+    // Downstream callers (e.g. credentialsd) move a CableQrCodeDevice across
+    // tokio::spawn boundaries, so both Send and Sync need to auto-derive.
+    const _: fn() = || {
+        fn assert_send_sync<T: Send + Sync>() {}
+        assert_send_sync::<CableQrCodeDevice>();
+    };
+
     #[test]
     fn qr_code_omits_key_6_for_cloud_assisted_only() {
         let device = CableQrCodeDevice::new_transient(