message: core: avoid unnecessary `format_args!` and `write!` macros
  This branch removes some unnecessary uses of the `format_args!`
  and `write!` macros in `tracing-core`. Using `fmt::Display::fmt` and
  similar rather than the macros may be slightly more efficient.
diff: @@ -214,7 +214,7 @@ pub trait Visit {
  #[cfg(feature = "std")]
  #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
  fn record_error(&mut self, field: &Field, value: &(dyn std::error::Error + 'static)) {
  - self.record_debug(field, &format_args!("{}", value))
  + self.record_debug(field, &DisplayValue(value))
  }
  /// Visit a value implementing `fmt::Debug`.
  @@ -499,19 +499,19 @@ where
  T: fmt::Display,
  {
  fn record(&self, key: &Field, visitor: &mut dyn Visit) {
  - visitor.record_debug(key, &format_args!("{}", self.0))
  + visitor.record_debug(key, self)
  }
  }
  impl<T: fmt::Display> fmt::Debug for DisplayValue<T> {
  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  - write!(f, "{}", self.0)
  + fmt::Display::fmt(self, f)
  }
  }
  impl<T: fmt::Display> fmt::Display for DisplayValue<T> {
  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  - fmt::Display::fmt(&self.0, f)
  + self.0.fmt(f)
  }
  }
  @@ -530,7 +530,7 @@ where
  impl<T: fmt::Debug> fmt::Debug for DebugValue<T> {
  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  - write!(f, "{:?}", self.0)
  + self.0.fmt(f)
  }
  }
  