QA: Aqua/JET findings marked @test_broken pending fix

The grouped-tests QA group (Aqua + JET) surfaces the following genuine findings. They are wrapped as @test_broken in test/qa/qa.jl so the QA group is green and the grouped-tests CI PR can merge; each should be fixed and then un-broken (the @test_broken reports "unexpectedly passing" once fixed, flagging the fix).

Aqua findings (failing sub-checks disabled in Aqua.test_all, marked @test_broken):

1. Undefined exports — 1. CatalystNetworkAnalysis.symbolic_steady_states is exported but Aqua flags it as undefined.

2. Stale dependencies — 4. Declared in [deps] but not loaded by the package: ReactionNetworkImporters, PolynomialRoots, ModelingToolkit, SBMLToolkit.

3. Compat bounds — extras. No [compat] entry for the Pkg extra (44cfe95a-1eb2-52ea-b672-e2afdf69b78f). Only the check_extras part of deps_compat is disabled; deps/weakdeps/julia compat checks still run and pass.

JET finding (marked @test_broken via report mode):

4. JET — 12 possible errors (JET.report_package(CatalystNetworkAnalysis; target_defined_modules = true)), e.g.:
   • Nemo.ZZMatrix(::SparseMatrixCSC{Int64,Int64}) no matching method (src/concordance.jl, src/deficiencytheory.jl).
   • undefined bindings: signconstraintmodel (src/concordance.jl:153), params (src/steadystates.jl:136), nv and edges (src/utils.jl).
   • no-matching-method: isweaklyreversible(::ReactionSystem[, ::Vector{ReactionSystem}]) (src/steadystates.jl), linkageclasses(::SimpleDiGraph) (src/utils.jl:4).

The other Aqua sub-checks pass (method ambiguity, unbound type params, project/test compare, deps/weakdeps/julia compat, piracy, persistent tasks).

Ignore until reviewed by @ChrisRackauckas.

Start in test/qa/qa.jl by reviewing the @test_broken cases, then run the listed Aqua.test_all checks and JET.report_package(CatalystNetworkAnalysis; target_defined_modules = true). Trace the reported issues in src/concordance.jl, src/deficiencytheory.jl, src/steadystates.jl, and src/utils.jl. Done means the findings are fixed, the wrappers are removed, and the grouped-tests QA remains green.