Type instability in Torus constructor

[lmh91]

This came up in #285.

The construction of a Torus is not entirely type stable as some parametric types of Torus depend on the values and not the types of the input arguments to the constructor:

@inferred CSG.Torus{Float64}(φ=π,θ=(π,2π)) # -> error

The parametric types which cause the issue are TT1 and TT2 of the Torus: https://github.com/SebastianRuffert/SolidStateDetectors.jl/blob/de2af27789cf8883f74ad0599acc60fc11aadd9a/src/ConstructiveSolidGeometry/VolumePrimitives/Torus.jl#L69. These define the types of two surfaces of the Torus. If we just remove TT1 and TT2 from the Torus we would shift the type instability into the function surfaces(t::Torus).

I think the best solution would be if we would came up with a way to remove the :inwards and :outwards parametric types of (all) surface primitives. Maybe by defining some field to those structs which only hold +1 or -1 in order to define the direction of surfaces like for the ConeMantle or TorusMantle.

However, we would still have the issue of the :flat case for the Torus. Here, one (or two) of the surfaces of the Torus become not a ConeMantle but an EllipticalSurface: see TorusThetaSurface. We would need to come up with a way to define these "flat" surfaces still as ConeMantle. In its current implementation of ConeMantle, this is not possible as hZ would be 0.