Add smoother setup stages

[termi-official]

The smoothers were not really doing what they should do and only worked in specific cases. This PR

1. add non-symmetric smoothers
2. adds scratches to the levels for the smoothers to precompute stuff
3. isolate some tests

[Abdelrahman912]

Also, I believe README file needs to be updated; to remove SOR smoother from the future section to the supported smoothers section.

[ViralBShah]

@termi-official Who might be able to help review and get this merged? This is a nice piece of work and I could use it in Circuitscape.jl for sure.

I've also invited you to this org.

[termi-official]

@Abdelrahman912 will make the review when I am done with the PR. Right now there is still a performance regression which I need to investigate in more detail.

[termi-official]

@Abdelrahman912 ready for review.

[Abdelrahman912]

Thanks @termi-official for the great effort. I left some comments about stuff that raises red flags from my pov. Other than this, this PR is fine from my side.

[ViralBShah]

I'm trying this PR with circuitscape, and get the following. Should I need to update to a new API (which I am happy to do)?

  107 dependencies successfully precompiled in 50 seconds. 103 already precompiled.
     Testing Running tests...
pwd = /Users/viral/.julia/dev/Circuitscape/test
Unit tests: Error During Test at /Users/viral/.julia/dev/Circuitscape/test/runtests.jl:11
  Got exception outside of a @test
  LoadError: FieldError: type AlgebraicMultigrid.MultiLevel has no field `presmoother`, available fields: `levels`, `final_A`, `coarse_solver`, `workspace`
  Stacktrace:
    [1] getproperty
      @ ./Base_compiler.jl:54 [inlined]
    [2] (::Circuitscape.var"#solve_pairs_for_point#solve##2"{Float64, Int64, Circuitscape.RasterFlags, CSConfig, Bool, Circuitscape.Shortcut{Float64}, Circuitscape.Cumulative{Float64, Int64}, Vector{Int64}, Vector{Tuple{Int64, Int64}}, Vector{Int64}, Vector{Int64}, Circuitscape.ComponentData{Float64, Int64}, AlgebraicMultigrid.Preconditioner{AlgebraicMultigrid.MultiLevel{AlgebraicMultigrid.Pinv{Float64}, SparseArrays.SparseMatrixCSC{Float64, Int64}, SparseArrays.SparseMatrixCSC{Float64, Int64}, LinearAlgebra.Adjoint{Float64, SparseArrays.SparseMatrixCSC{Float64, Int64}}, AlgebraicMultigrid.MultiLevelWorkspace{Vector{Float64}, 1}}, AlgebraicMultigrid.V}, SparseArrays.SparseMatrixCSC{Float64, Int64}, Vector{Int64}})(point_idx::Int64, local_timer::TimerOutputs.TimerOutput)
      @ Circuitscape ~/.julia/dev/Circuitscape/src/core.jl:178
    [3] solve(prob::Circuitscape.GraphProblem{Float64, Int64, Circuitscape.AMGSolver}, ::Circuitscape.AMGSolver, flags::Circuitscape.RasterFlags, cfg::CSConfig, log::Bool)
      @ Circuitscape ~/.julia/dev/Circuitscape/src/core.jl:259
    [4] single_ground_all_pairs
      @ ~/.julia/dev/Circuitscape/src/core.jl:71 [inlined]

[termi-official]

It seems like you are on an old commit of the PR. Can you check if you are on c4a51b5 ?

[ViralBShah]

Ah yes indeed. All tests are now passing.

[Abdelrahman912]

Other than the following two comments, the PR is ready.