Canonical CI: grouped-tests.yml + root test/test_groups.toml

[ChrisRackauckas-Claude]

Converts the root test workflow (CI.yml) to the canonical thin caller that dispatches to SciML/.github grouped-tests.yml@v1, with the version × group matrix declared once in test/test_groups.toml.

What changed

• .github/workflows/CI.yml: the hand-maintained matrix test job is replaced by a thin caller of grouped-tests.yml@v1. on: and concurrency: are preserved verbatim; name: CI kept. Uses group-env-name: PPS_TEST_GROUP.
• test/test_groups.toml (new, root): declares the matrix — [Core] on lts, 1, pre; [QA] on lts, 1. Linux-only (no os axis).
• Category B refactor (JET ran inline): the JET static-analysis block is moved out of the always-on functional suite into a dedicated QA group, isolated in test/qa/Project.toml (JET + StaticArrays + Test + the package via [sources] path ../.., julia = "1.10") with test/qa/qa.jl (verbatim from the old test/jet.jl). runtests.jl activates that env, develops the package, instantiates, and includes qa.jl when the group is QA; otherwise it runs the functional tests (regression, reinit, CPU optimizer/constraints/lbfgs) as before. test/jet.jl removed.
• Group dispatch env var: uses a dedicated PPS_TEST_GROUP rather than the default GROUP, because GROUP is already consumed by GPU.yml and the buildkite pipeline for backend selection (CUDA/AMDGPU). runtests.jl still reads GROUP for backend selection within the Core group, so those workflows are untouched.
• Root Project.toml metadata fixes: added missing [compat] entries for the test-only stdlibs LinearAlgebra and Test (both listed in [extras]). julia compat already at the 1.10 LTS floor — left unchanged.

Only CI.yml was modified among workflows; Downgrade.yml, GPU.yml, FormatCheck.yml, SpellCheck.yml, TagBot.yml, etc. are untouched.

Matrix match

The emitted (group, version, runner) set from compute_affected_sublibraries.jl --root-matrix:

Core: (lts, 1, pre) × ubuntu-latest
QA:   (lts, 1)      × ubuntu-latest

The previous CI.yml ran a single cell (version: "1", whole suite incl. JET). That cell is preserved (Core 1 + QA 1); the canonical conversion additionally adds lts + pre to the functional group and lts to QA. All Linux, matching the Linux-only previous setup.

Verification (static only)

• Ran compute_affected_sublibraries.jl . --root-matrix (Julia 1.11) — reproduces the matrix above.
• TOML parse of test/test_groups.toml, test/qa/Project.toml, root Project.toml — all OK; all [extras] deps now have [compat] entries.
• YAML parse of CI.yml — OK.
• Did not instantiate or run tests / Aqua / JET locally (structural conversion only).

QA group is newly wired; Aqua/JET run in CI — any failures will be triaged in a follow-up.

Ignore until reviewed by @ChrisRackauckas.