QA: scan PureKLUForwardDiffExt (load ForwardDiff in the QA env)

[ChrisRackauckas-Claude]

Please ignore this PR until reviewed by @ChrisRackauckas.

Problem

SciMLTesting.run_qa runs ExplicitImports over the package's submodules. ExplicitImports does know about extensions — it reads the [extensions] table out of Project.toml — but it skips any extension whose module does not exist:

ext_mod = Base.get_extension(mod, Symbol(ext))
ext_mod === nothing && continue

An extension module only exists once its trigger weakdep is loaded, and the QA environment never loaded ForwardDiff. So PureKLUForwardDiffExt was getting zero ExplicitImports coverage, while QA reported a clean pass.

Fix

• Add ForwardDiff to test/qa/Project.toml ([deps] + [compat] = "1", mirroring the root compat).
• using ForwardDiff in test/qa/qa.jl before run_qa, with a comment explaining why.

Proof the extension is now actually scanned

A passing QA summary is not proof — each ExplicitImports check folds every submodule into one @test, so a clean extension yields an identical summary either way. Direct check from test/qa:

=== WITH ForwardDiff loaded (this PR) ===
get_extension(PureKLU, :PureKLUForwardDiffExt) => PureKLUForwardDiffExt
modules scanned: Module[PureKLUForwardDiffExt, PureKLU, PureKLU.AMD, PureKLU.BTF]

=== WITHOUT ForwardDiff loaded (main today) ===
get_extension(PureKLU, :PureKLUForwardDiffExt) => nothing
modules scanned: Module[PureKLU, PureKLU.AMD, PureKLU.BTF]

Findings surfaced, and what was done with each

Turning the scan on produced 3 errored checks. All were addressed:

Fixed in source (not ignored):

1. no_stale_explicit_imports — AbstractKLUFactorization was imported by ext/PureKLUForwardDiffExt.jl and never used. Removed from the import list.
2. all_explicit_imports_are_public — KLUFactorization is not public in PureKLU. It is documented API (it is what klu returns, and it has a @docs entry in docs/src/api.md), it just was never declared public. Declared it in src/PureKLU.jl, guarded for the 1.10 LTS where the public keyword does not exist. It deliberately stays unexported, since KLU.jl exports the same name and PureKLU is a drop-in for it. This adds public API, hence the 1.2.0 → 1.3.0 minor bump.

Ignored, with justification:

3. all_explicit_imports_are_public / all_qualified_accesses_are_public — ForwardDiff.Dual, ForwardDiff.Partials, ForwardDiff.value, ForwardDiff.partials. ForwardDiff v1 declares no name public and exports none of its dual-number interface (names(ForwardDiff) == [:DiffResults, :ForwardDiff]), so there is no public spelling for the types and accessors any AD extension must dispatch on and unpack. Added as a single commented FORWARDDIFF_NONPUBLIC tuple applied to both public-API checks. No check was disabled and nothing was marked @test_broken.

Coverage

• Now scanned: PureKLUForwardDiffExt (the package's only extension).
• Still unscanned: none.

Local results

$ GROUP=QA julia --project=. -e 'using Pkg; Pkg.test()'
Test Summary: | Pass  Total   Time
QA/qa.jl      |   20     20  39.4s
     Testing PureKLU tests passed

GROUP=Core also run, to confirm the extension edit and the public declaration break nothing:

Core/test_allocations.jl        |   16
Core/test_check_false.jl        |    8
Core/test_compare_klu.jl        |  710
Core/test_fma_on.jl             |  396
Core/test_full_factor_false.jl  |    4
Core/test_fully_preallocated.jl |   40
Core/test_generic_eltypes.jl    |  167
Core/test_interfaces.jl         |   10
Core/test_issue4.jl             |    1
Core/test_klu_wrappers.jl       |  137
Core/test_phases.jl             |  678
Core/test_singular_fastexit.jl  |   56
     Testing PureKLU tests passed

(Julia 1.12, ForwardDiff v1.4.3.)

Also gitignored test/qa/Manifest.toml, which the QA run generates.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Yb5kCpT5SRzTrhppKSh1n7