Used only as no-op for macros in feature-dependent deps.

Can be removed once https://github.com/rust-lang/rust/issues/64797 is available on stable.

```rust

[cfg(feature = "typetag")]

pub use typetag::serde as typetag_serde;

[cfg(not(feature = "typetag"))]

pub use entitynoopmacros::noopattr as typetagserde; ```