fixup! Add generic config mechanism

Simplify GetConfig response

src/config.rs

@@ -1,6 +1,9 @@
-use core::str::FromStr;
+use core::{
+    fmt::{self, Display, Formatter, Write as _},
+    str::FromStr,
+};
 
-use cbor_smol::{cbor_deserialize, cbor_serialize_bytes, Bytes};
+use cbor_smol::{cbor_deserialize, cbor_serialize_bytes};
 use littlefs2::{path, path::Path};
 use serde::{de::DeserializeOwned, Serialize};
 use trussed::{
@@ -43,6 +46,15 @@ impl<'a> ConfigValueMut<'a> {
     }
 }
 
+impl<'a> Display for ConfigValueMut<'a> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Bool(value) => write!(f, "{}", value),
+            Self::U8(value) => write!(f, "{}", value),
+        }
+    }
+}
+
 #[derive(Debug)]
 #[repr(u8)]
 pub enum ConfigError {
@@ -69,13 +81,7 @@ pub fn get<C: Config, const N: usize>(
     response: &mut Vec<u8, N>,
 ) -> Result<(), ConfigError> {
     let field = config.field(key).ok_or(ConfigError::InvalidKey)?;
-    // TODO: reuse response buffer -- does not work out of the box because we have Vec<u8, _>
-    // and cbor-smol expects Bytes<_>
-    let data: Bytes<N> =
-        cbor_serialize_bytes(&field).map_err(|_| ConfigError::SerializationFailed)?;
-    response
-        .extend_from_slice(&data)
-        .map_err(|_| ConfigError::DataTooLong)
+    write!(response, "{}", field).map_err(|_| ConfigError::DataTooLong)
 }
 
 pub fn set<C: Config>(config: &mut C, key: &str, value: &str) -> Result<(), ConfigError> {