fix isless(U1)

Author: ogauthe

NDTensors/src/lib/SymmetrySectors/src/sector_definitions/u1.jl

@@ -28,3 +28,4 @@ end
 
 # enforce U1(Int32(1)) == U1(1)
 Base.:(==)(s1::U1, s2::U1) = sector_label(s1) == sector_label(s2)
+Base.isless(s1::U1, s2::U1) = sector_label(s1) < sector_label(s2)

NDTensors/src/lib/SymmetrySectors/test/test_simple_sectors.jl

@@ -50,6 +50,7 @@ using Test: @inferred, @test, @testset, @test_throws
     @test TrivialSector() == U1(0)
     @test U1(-1) < TrivialSector()
     @test TrivialSector() < U1(1)
+    @test U1(Int8(1)) < U1(Int32(2))
   end
 
   @testset "Z₂" begin