[BUG] Base state for photons is not correct

[szabo137]

It seems like the base state of incoming and outgoing photons for PolY is wrong regarding the azimuthal angle:

julia> using QEDbase

julia> using Test

julia> function test_ortho(phi)
           om = 1.0
           cth, sth = 0.0, 1.0
           sphi,cphi = sincos(phi)
           K = SFourMomentum(om,om*sth*cphi,om*sth*sphi,om*cth)

           eps= base_state(
                   Photon(),
                   Outgoing(),
                   K,
                   PolY()
               )

           return K*eps
       end
test_ortho (generic function with 1 method)

julia> @test isapprox(test_ortho(pi/2*0.9),0.0,atol=eps())
Test Passed

julia> @test isapprox(test_ortho(pi/2*1.01),0.0,atol=eps())
Test Failed at REPL[23]:1
  Expression: isapprox(test_ortho((pi / 2) * 1.01), 0.0, atol = eps())
   Evaluated: isapprox(-0.03141075907812746, 0.0; atol = 2.220446049250313e-16)

ERROR: There was an error during testing

It seems like, for $\phi\in [0,\pi/2]$ and $\phi\in [3/2\pi,2\pi]$ everything is alright, but for $\phi\in [\pi/2,3/2\pi]$ the y-pol state is not orthogonal to the respective four-momentum.