feat: require at least 128 bits of entropy

crates/util/keyfork-entropy/src/main.rs

@@ -14,6 +14,10 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         bit_size <= 256,
         "Maximum supported bit size is 256, got: {bit_size}"
     );
+    assert!(
+        bit_size >= 128,
+        "Minimum supported bit size is 128, got {bit_size}"
+    );
 
     let entropy = keyfork_entropy::generate_entropy_of_size(bit_size / 8)?;
     println!("{}", smex::encode(entropy));