Roll out SciMLTesting.jl: replace copied test-harness boilerplate across SciML repos

[ChrisRackauckas-Claude]

Roll out SciMLTesting.jl across SciML packages

SciMLTesting.jl is a new, lightweight package that holds the shared test-harness helpers that are currently copy-pasted into every SciML monorepo's runtests.jl. The goal of this issue is to track converting repos to depend on it instead of duplicating the boilerplate.

What it is

• Repo: https://github.com/SciML/SciMLTesting.jl — UUID 09d9d899-5365-40a9-917a-5f67fddea283, v0.1.0.
• Registration: New package: SciMLTesting v0.1.0 JuliaRegistries/General#157424 (new-package 3-day window; auto-merges ~2026-06-11, then TagBot tags v0.1.0).
• Light by design — [deps] = Pkg, TOML, Test only. Aqua/JET are not hard deps; run_qa takes the loaded modules as kwargs so consumers don't inherit them.
• Tested green on Julia 1.10 (LTS floor) and 1.11.

Exported API (replaces the copied boilerplate)

Helper	Replaces
current_group(; env="GROUP", default="All")	const GROUP = get(ENV, "GROUP", "All")
activate_group_env(group_dir; parent=…, develop=true, instantiate=true)	the copied activate_qa_env / activate_examples_env / activate_downstream_env (parent accepts a path or an iterable for monorepo sublibs)
run_qa(pkg; Aqua=…, JET=…, aqua=true, jet=false, …)	the copied Aqua.test_all / JET.test_package QA-group body
detect_sublibrary_group(group, lib_dir; default_group="Core") → (sublibrary, test_group)	the copied _detect_sublibrary_group monorepo dispatcher

Rollout — what needs to be done

Once #157424 merges and v0.1.0 is tagged:

• Add SciMLTesting to each target repo's [extras] + [targets].test (and sublib [extras]/[targets].test for monorepos).
• Replace the copied boilerplate in test/runtests.jl (and lib/*/test/runtests.jl) with using SciMLTesting + the four calls.
• OrdinaryDiffEq.jl first as the reference conversion, then the other 10 canonicalized monorepos (BoundaryValueDiffEq, Corleone, DataDrivenDiffEq, DiffEqProblemLibrary, LinearSolve, NeuralLyapunov, NonlinearSolve, Optimization, OptimalUncertaintyQuantification, RecursiveArrayTools), then standalone packages as convenient.
• One draft PR per repo, static-verified (don't run full suites), marked ignore-until-reviewed.

Known non-goal / follow-up

• The Julia-<1.11 transitive [sources] develop walk was intentionally left per-repo (it's repo-shaped). If we want it shared too, it could become an optional develop_sources!(dir) helper in a later SciMLTesting minor.

Ignore until reviewed by @ChrisRackauckas.