`Type.Id`

Type identifiers (available in OCaml 5.1).

A type identifier is a value that denotes a type. Given two type identifiers, they can be tested for equality to prove they denote the same type. Note that:

- Unequal identifiers do not imply unequal types: a given type can be denoted by more than one identifier.
- Type identifiers can be marshalled, but they get a new, distinct, identity on unmarshalling, so the equalities are lost.