`spinmatrices` is too restrictive on its input type

[ogauthe]

Hi!

using HalfIntegers:half
using TensorKit
using MPSKitModels: S_exchange

sds = S_exchange(Float64, Trivial; spin=half(1))  # MethodError
sds = S_exchange(Float64, Trivial; spin=0.5)  # MethodError

ERROR: MethodError: no method matching spinmatrices(::HalfIntegers.Half{Int64}, ::Type{ComplexF64})

Closest candidates are:
  spinmatrices(::Union{Rational{Int64}, Int64}, ::Any)
   @ MPSKitModels ~/.julia/packages/MPSKitModels/abQMO/src/operators/spinoperators.jl:20

Stacktrace:
 [1] S_x(elt::Type{ComplexF64}, ::Type{Trivial}; spin::HalfIntegers.Half{Int64})
   @ MPSKitModels ~/.julia/packages/MPSKitModels/abQMO/src/operators/spinoperators.jl:63
 [2] S_plus(elt::Type{ComplexF64}, ::Type{Trivial}; spin::HalfIntegers.Half{Int64})
   @ MPSKitModels ~/.julia/packages/MPSKitModels/abQMO/src/operators/spinoperators.jl:257
 [3] S_plusmin(elt::Type{ComplexF64}, ::Type{Trivial}; spin::HalfIntegers.Half{Int64})
   @ MPSKitModels ~/.julia/packages/MPSKitModels/abQMO/src/operators/spinoperators.jl:408
 [4] S_exchange(elt::Type{Float64}, symmetry::Type{Trivial}; spin::HalfIntegers.Half{Int64})
   @ MPSKitModels ~/.julia/packages/MPSKitModels/abQMO/src/operators/spinoperators.jl:452
 [5] top-level scope
   @ REPL[44]:1