message: Optimise string to JSON conversion
  Summary: Before we allocated and filled a buffer very efficiently. Then we reallocated and copied it entirely to add the leading/trailing quote characters. Don't do that.
diff: @@ -78,7 +78,8 @@ pub(crate) fn hash_string_value<H: Hasher>(x: &str, state: &mut H) {
  }
  pub(crate) fn json_escape(x: &str) -> String {
  - let mut escaped = Vec::with_capacity(x.len());
  + let mut escaped = Vec::with_capacity(x.len() + 2);
  + escaped.push(b'\"');
  for c in x.bytes() {
  // Escape as per ECMA-404 standard
  match c {
  @@ -93,7 +94,8 @@ pub(crate) fn json_escape(x: &str) -> String {
  x => escaped.push(x),
  }
  }
  - unsafe { format!("\"{}\"", String::from_utf8_unchecked(escaped)) }
  + escaped.push(b'\"');
  + unsafe { String::from_utf8_unchecked(escaped) }
  }
  impl SimpleValue for Box<str> {}
  