message: Add Trace for Either
  Summary: Useful to have
diff: @@ -32,6 +32,7 @@ use std::sync::atomic::AtomicUsize;
  use std::sync::Arc;
  use std::sync::Mutex;
  +use either::Either;
  use hashbrown::raw::RawTable;
  use crate::collections::SmallMap;
  @@ -158,6 +159,15 @@ unsafe impl<'v, T1: Trace<'v>, T2: Trace<'v>, T3: Trace<'v>, T4: Trace<'v>> Trac
  }
  }
  +unsafe impl<'v, T1: Trace<'v>, T2: Trace<'v>> Trace<'v> for Either<T1, T2> {
  + fn trace(&mut self, tracer: &Tracer<'v>) {
  + match self {
  + Either::Left(x) => x.trace(tracer),
  + Either::Right(x) => x.trace(tracer),
  + }
  + }
  +}
  +
  unsafe impl<'v> Trace<'v> for Value<'v> {
  fn trace(&mut self, tracer: &Tracer<'v>) {
  tracer.trace(self)
  