feat(measure_theory/group/geometry_of_numbers): Blichfeldt and Minkowski's theorems (#2819)
I had a go at Minkowski's convex body theorem and it works thanks to @urkud 's pidgeonhole for measurable spaces.
Co-authored-by: Yaël Dillies <yael.dillies@gmail.com>
Co-authored-by: Xavier-François Roblot <46200072+xroblot@users.noreply.github.com>
Co-authored-by: RemyDegenne <Remydegenne@gmail.com>