add feature flags to prevent needless warnings when nts-pool is disabled

ntp-proto/src/packet/crypto.rs

@@ -150,11 +150,13 @@ impl AesSivCmac256 {
         AesSivCmac256 { key }
     }
 
+    #[cfg(feature = "nts-pool")]
     pub fn key_size() -> usize {
         // prefer trust in compiler optimisation over trust in mental arithmetic
         Self::new(Default::default()).key.len()
     }
 
+    #[cfg(feature = "nts-pool")]
     pub fn from_key_bytes(key_bytes: &[u8]) -> Result<Self, KeyError> {
         (key_bytes.len() == Self::key_size())
             .then(|| Self::new(*aead::Key::<Aes128Siv>::from_slice(key_bytes)))
@@ -233,11 +235,13 @@ impl AesSivCmac512 {
         AesSivCmac512 { key }
     }
 
+    #[cfg(feature = "nts-pool")]
     pub fn key_size() -> usize {
         // prefer trust in compiler optimisation over trust in mental arithmetic
         Self::new(Default::default()).key.len()
     }
 
+    #[cfg(feature = "nts-pool")]
     pub fn from_key_bytes(key_bytes: &[u8]) -> Result<Self, KeyError> {
         (key_bytes.len() == Self::key_size())
             .then(|| Self::new(*aead::Key::<Aes256Siv>::from_slice(key_bytes)))
@@ -461,6 +465,7 @@ mod tests {
         assert_eq!(result, (0..16).collect::<Vec<u8>>());
     }
 
+    #[cfg(feature = "nts-pool")]
     #[test]
     fn key_functions_correctness() {
         use aead::KeySizeUser;