Depend on serde_core instead of serde

This crate does not make use of serde derive macros, thus it can
depend on `serde_core` instead of `serde` to speed up users' compile
times.

See the documentation of [`serde_core`](https://docs.rs/serde_core)
for more details.

Note that this adds a hidden `serde_core` feature, since we cannot use
the `dep:` syntax when declaring the `serde` feature due to this crate's
MSRV being lower than [the required 1.60](https://blog.rust-lang.org/2022/04/07/Rust-1.60.0/#new-syntax-for-cargo-features).

Author: DaniPopes

Cargo.toml

@@ -21,9 +21,10 @@ categories = ["network-programming", "data-structures"]
 [features]
 default = ["std"]
 std = []
+serde = ["serde_core"]
 
 [dependencies]
-serde = { version = "1.0.60", optional = true, default-features = false, features = ["alloc"] }
+serde_core = { version = "1.0.221", optional = true, default-features = false, features = ["alloc"] }
 # Use portable-atomic crate to support platforms without atomic CAS.
 # See "no_std support" section in readme for more information.
 #

src/serde.rs

@@ -2,7 +2,7 @@ use super::{Bytes, BytesMut};
 use alloc::string::String;
 use alloc::vec::Vec;
 use core::{cmp, fmt};
-use serde::{de, Deserialize, Deserializer, Serialize, Serializer};
+use serde_core::{de, Deserialize, Deserializer, Serialize, Serializer};
 
 macro_rules! serde_impl {
     ($ty:ident, $visitor_ty:ident, $from_slice:ident, $from_vec:ident) => {