Exclude encoding::Decodable from mutation testing

Recently added encoding::Decodable impls construct a new decoder.
Mutation testing replaces these with Default::default(), which is
equivalent to the intended new().

Exclude these from mutation testing to avoid false positives.

Author: jamillambert

.cargo/mutants.toml

@@ -11,6 +11,7 @@ exclude_re = [
     "deserialize", # Skip serde mutation tests
     "serde_details::<impl de::Visitor<'_>", # Skip serde mutation tests
     "Iterator", # Mutating operations in an iterator can result in an infinite loop
+    "impl encoding::Decodable", # Mutant replacing Default::default() is equivalent to returning new()
 
     # ----------------------------------Crate-specific exclusions----------------------------------
     # Units