message: Make record a bit smaller
  Summary:
  Saves a little memory, but practically not much.
  However, we should allocate record data in starlark heap, not in malloc.
diff: @@ -152,7 +152,7 @@ pub type FrozenRecordType = RecordTypeGen<FrozenValue, Option<String>>;
  #[repr(C)]
  pub struct RecordGen<V> {
  typ: V, // Must be RecordType
  - values: Vec<V>,
  + values: Box<[V]>,
  }
  impl<'v, V: ValueLike<'v>> Display for RecordGen<V> {
  @@ -308,7 +308,10 @@ where
  };
  values.push(value);
  }
  - Ok(eval.heap().alloc_complex(Record { typ: this, values }))
  + Ok(eval.heap().alloc_complex(Record {
  + typ: this,
  + values: values.into_boxed_slice(),
  + }))
  })
  }
  @@ -411,7 +414,7 @@ where
  fn write_hash(&self, hasher: &mut StarlarkHasher) -> anyhow::Result<()> {
  self.typ.write_hash(hasher)?;
  - for v in &self.values {
  + for v in &*self.values {
  v.write_hash(hasher)?;
  }
  Ok(())
  