fix: hex compatibility (#244)

crates/primitives/Cargo.toml

@@ -66,3 +66,7 @@ arbitrary = [
     "dep:proptest",
     "dep:proptest-derive",
 ]
+
+# `const-hex` compatibility feature for `hex`.
+# Should not be needed most of the time.
+hex-compat = ["hex/hex"]

crates/primitives/src/bits/macros.rs

@@ -375,7 +375,9 @@ macro_rules! impl_fb_traits {
             where
                 T: $crate::private::AsRef<[u8]>
             {
-                $crate::hex::FromHex::from_hex(hex).map(Self)
+                let mut buf = [0u8; $n];
+                $crate::hex::decode_to_slice(hex.as_ref(), &mut buf)?;
+                Ok(Self::new(buf))
             }
         }
     };