refactor: collect parameters such that they are type stable

[sathvikbhagavan]

Followup of #304 - Checked type inference of all methods and found some instabilities like:

julia> @inferred CubicSpline(u, t)
ERROR: return type CubicSpline{ReadOnlyArrays.ReadOnlyVector{Float64, Vector{Float64}}, ReadOnlyArrays.ReadOnlyVector{Float64, Vector{Float64}}, Vector{Float64}, Vector{Float64}, Vector{Float64}, Vector{Float64}, Float64} does not match inferred return type CubicSpline{ReadOnlyArrays.ReadOnlyVector{Float64, Vector{Float64}}, ReadOnlyArrays.ReadOnlyVector{Float64, Vector{Float64}}, _A, _B, Vector{Float64}, Vector{Float64}, Float64} where {_A, _B}
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:35
 [2] top-level scope
   @ REPL[6]:1

Analyzed using Cthulhu and found instability was in the construction of parameter cache.

I have fixed and added all the inference tests.

[ChrisRackauckas]

Suggested change

	l₀, l₁, l₂ = collect.(eachrow(reduce(hcat, collect.(parameters))))
	l₀, l₁, l₂ = collect.(eachrow(stack(collect.(parameters)))

[sathvikbhagavan]

Addressed in 826f0a7