Add mutation excludes for impl encoding::Decoder

The min_byte_needed function is a simple cast for optimization and does
not need to be tested.

Add a mutation testing exclude for all of these functions.

Author: jamillambert

.cargo/mutants.toml

@@ -12,6 +12,7 @@ exclude_re = [
     "serde_details::<impl de::Visitor<'_>", # Skip serde mutation tests
     "Iterator", # Mutating operations in an iterator can result in an infinite loop
     "<impl encoding::Decodable for .*>::decoder", # Mutant replacing Default::default() is equivalent to returning new()
+    "<impl encoding::Decoder for .*>::min_bytes_needed", # Function is just a cast for optimization.
 
 
     # ----------------------------------Crate-specific exclusions----------------------------------