replace bytes::find with memchr::memmem::find

This is a much more efficient implementation with ~20% improved
throughput and latency with the simple signing benchmark.

signing/sign            time:   [1.3024 ms 1.3050 ms 1.3076 ms]
                        thrpt:  [2.2886 MiB/s 2.2933 MiB/s 2.2978 MiB/s]
                 change:
                        time:   [-19.016% -18.855% -18.691%] (p = 0.00 < 0.05)
                        thrpt:  [+22.987% +23.237% +23.482%]
                        Performance has improved.

Cargo.lock

@@ -131,6 +131,7 @@ dependencies = [
  "futures",
  "indexmap",
  "mailparse",
+ "memchr",
  "nom",
  "quick-error 2.0.1",
  "regex",

Cargo.toml

@@ -14,6 +14,7 @@ license = "MIT"
 [dependencies]
 ed25519-dalek = "1.0.1"
 mailparse = "0.14"
+memchr = "2.5"
 quick-error = "2.0.1"
 nom = "7.1.0"
 chrono = { version = "0.4.19", default-features = false, features = ["clock", "std"] }

src/bytes.rs

@@ -1,4 +1,5 @@
 ///! Various utility functions to operate on bytes
+pub(crate) use memchr::memmem::find;
 
 pub(crate) fn get_all_after<'a>(bytes: &'a [u8], end: &[u8]) -> &'a [u8] {
     if let Some(mut end_index) = find(bytes, end) {
@@ -9,13 +10,6 @@ pub(crate) fn get_all_after<'a>(bytes: &'a [u8], end: &[u8]) -> &'a [u8] {
     }
 }
 
-/// Find the offset of specific bytes in bytes
-pub(crate) fn find(bytes: &[u8], search: &[u8]) -> Option<usize> {
-    bytes
-        .windows(search.len())
-        .position(|window| window == search)
-}
-
 pub(crate) fn replace(bytes: &mut [u8], from: char, to: char) {
     for byte in bytes.iter_mut() {
         if *byte == from as u8 {