Drop KrylovPreconditioners test dependency (#1097)

Use a public LinearAlgebra diagonal inverse in the existing preconditioner and reuse tests so downgrade resolution no longer needs a package-specific exception.

Co-authored-by: ChrisRackauckas-Claude <accounts@chrisrackauckas.com>

Author: ChrisRackauckas-Claude

.github/workflows/Downgrade.yml

@@ -17,6 +17,4 @@ jobs:
     with:
       julia-version: "lts"
       group: "Core"
-      # Resolver.jl cannot minimum-resolve KrylovPreconditioners' historical Arpack/LightGraphs graph.
-      no_promote: "Mooncake,KrylovPreconditioners"
     secrets: "inherit"

Project.toml

@@ -151,7 +151,6 @@ JacobiDavidson = "0.1"
 KernelAbstractions = "0.9.30"
 Krylov = "0.10"
 KrylovKit = "0.10"
-KrylovPreconditioners = "0.3"
 LAPACK_jll = "3"
 Libdl = "1.10"
 LinearAlgebra = "1.10"
@@ -214,7 +213,6 @@ InteractiveUtils = "b77e0a4c-d291-57a0-90e8-8db25a27a240"
 IterativeSolvers = "42fd0dbc-a981-5370-80f2-aaf504508153"
 JacobiDavidson = "11c68b98-9c9b-11e8-267b-bbb95576cead"
 KrylovKit = "0b1a1467-8014-51b9-945f-bf0ae24f4b77"
-KrylovPreconditioners = "45d422c2-293f-44ce-8315-2cb988662dec"
 MultiFloats = "bdf0d083-296b-4888-a5b6-7498122e68a5"
 Pkg = "44cfe95a-1eb2-52ea-b672-e2afdf69b78f"
 PureUMFPACK = "b7e1f0a2-3c4d-4e5f-9a0b-1c2d3e4f5a6b"
@@ -232,4 +230,4 @@ Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 Zygote = "e88e6eb3-aa80-5325-afca-941959d7151f"
 
 [targets]
-test = ["AlgebraicMultigrid", "Arpack", "ArnoldiMethod", "BandedMatrices", "BlockDiagonals", "CliqueTrees", "ComponentArrays", "FastAlmostBandedMatrices", "FastLapackInterface", "FiniteDiff", "FixedSizeArrays", "ForwardDiff", "InteractiveUtils", "IterativeSolvers", "JacobiDavidson", "KrylovKit", "KrylovPreconditioners", "MultiFloats", "Pkg", "PureUMFPACK", "Random", "RecursiveFactorization", "STRUMPACK_jll", "SafeTestsets", "SciMLTesting", "SparseArrays", "Sparspak", "SpecializingFactorizations", "StableRNGs", "StaticArrays", "Test", "Zygote"]
+test = ["AlgebraicMultigrid", "Arpack", "ArnoldiMethod", "BandedMatrices", "BlockDiagonals", "CliqueTrees", "ComponentArrays", "FastAlmostBandedMatrices", "FastLapackInterface", "FiniteDiff", "FixedSizeArrays", "ForwardDiff", "InteractiveUtils", "IterativeSolvers", "JacobiDavidson", "KrylovKit", "MultiFloats", "Pkg", "PureUMFPACK", "Random", "RecursiveFactorization", "STRUMPACK_jll", "SafeTestsets", "SciMLTesting", "SparseArrays", "Sparspak", "SpecializingFactorizations", "StableRNGs", "StaticArrays", "Test", "Zygote"]

test/Core/basictests.jl

@@ -1,7 +1,7 @@
 using LinearSolve, LinearAlgebra, SparseArrays, MultiFloats, ForwardDiff
 using SciMLOperators: SciMLOperators, MatrixOperator, FunctionOperator, WOperator
 using RecursiveFactorization, Sparspak, FastLapackInterface
-using IterativeSolvers, KrylovKit, MKL_jll, KrylovPreconditioners
+using IterativeSolvers, KrylovKit, MKL_jll
 using Test
 import CliqueTrees, Random
 
@@ -481,7 +481,7 @@ end
 
     @testset "KrylovJL" begin
         kwargs = (; gmres_restart = 5)
-        precs = (A, p = nothing) -> (BlockJacobiPreconditioner(A, 2), I)
+        precs = (A, p = nothing) -> (Diagonal(inv.(diag(A))), I)
         algorithms = (
             ("Default", KrylovJL(; kwargs...)),
             ("CG", KrylovJL_CG(; kwargs...)),
@@ -507,7 +507,7 @@ end
 
         function countingprecs(A, p = nothing)
             num_precs_calls += 1
-            (BlockJacobiPreconditioner(A, 2), I)
+            (Diagonal(inv.(diag(A))), I)
         end
 
         n = 10