need to ensure operations involving the constants defined here keep constant folding

[nsajko]

The PR JuliaLang/julia#55886 stripped generic AbstractIrrational operations of their effect annotations. As a bugfix, it will be part of future v1.10, v1.11 and v1.12 Julia releases. This means that operations like Rational{Int}(twoπ) won't constant fold.

There are several possible fixes for this issue, including defining effect annotations in this package, or, in some cases, hardcoding the return values.

[devmotion]

We could just add it to the macro, that's the only official way for defining new irrational constants anyway.