Test Go 1.27 generic methods with a compiler boundary
A new Go language feature can be easy to demonstrate and still be awkward to introduce. Generic methods in Go 1.27 are a good example. They let a concrete type declare type parameters on one of its methods, which can move an operation back beside the type it operates on. That is useful for a pipeline, collection, or builder API. It is also a source-level compatibility boundary: the same declaration is rejected by a Go 1.26 compiler.