Remove flexibility of BSplineManifold

[hyrodium]

julia> using BasicBSpline

julia> P1 = BSplineSpace{2, Int}(knotvector"3 113")
BSplineSpace{2, Int64, KnotVector{Int64}}(KnotVector([1, 1, 1, 3, 4, 5, 5, 5]))

julia> P2 = BSplineSpace{2, Rational{Int}}(knotvector"3 113")
BSplineSpace{2, Rational{Int64}, KnotVector{Rational{Int64}}}(KnotVector(Rational{Int64}[1//1, 1//1, 1//1, 3//1, 4//1, 5//1, 5//1, 5//1]))

julia> a = rand(dim(P1), dim(P2))
5×5 Matrix{Float64}:
 0.795926   0.306069  0.308997  0.495476   0.305326
 0.0126793  0.416423  0.842358  0.468503   0.755102
 0.815584   0.862331  0.4443    0.931929   0.546555
 0.273801   0.606731  0.278222  0.530024   0.286829
 0.474029   0.589485  0.611897  0.0475267  0.661962

julia> bsplinespaces(BSplineManifold(a, P1, P2))[1]
BSplineSpace{2, Int64, KnotVector{Int64}}(KnotVector([1, 1, 1, 3, 4, 5, 5, 5]))

julia> bsplinespaces(BSplineManifold(a, P1, P2))[2]
BSplineSpace{2, Rational{Int64}, KnotVector{Rational{Int64}}}(KnotVector(Rational{Int64}[1//1, 1//1, 1//1, 3//1, 4//1, 5//1, 5//1, 5//1]))

bsplinespaces(BSplineManifold(a, P1, P2))[1] can be BSplineSpace{2, Rational{Int64}} for simplicity.