Support simd_json (#105)

This PR adds support for the simd-json library whenever decoding or encoding JSON responses. This may be enabled independently of serenity and twilight support for SIMD acceleration.

Co-authored-by: Kyle Simpson <kyleandrew.simpson@gmail.com>

src/input/codecs/dca/mod.rs

@@ -110,9 +110,11 @@ impl FormatReader for DcaReader {
                 return symph_err::decode_error("missing DCA1 metadata block");
             }
 
-            let raw_json = source.read_boxed_slice_exact(size as usize)?;
+            let mut raw_json = source.read_boxed_slice_exact(size as usize)?;
 
-            let metadata: DcaMetadata = serde_json::from_slice::<DcaMetadata>(&raw_json)
+            // NOTE: must be mut for simd-json.
+            #[allow(clippy::unnecessary_mut_passed)]
+            let metadata: DcaMetadata = crate::json::from_slice::<DcaMetadata>(&mut raw_json)
                 .map_err(|_| SymphError::DecodeError("malformed DCA1 metadata block"))?;
 
             let mut revision = MetadataBuilder::new();