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

[ChrisRackauckas-Claude]

Summary

Converts the root Tests.yml test workflow into a thin caller of the canonical SciML/.github grouped-tests.yml@v1 reusable workflow, with the package's group × version matrix declared once in a root test/test_groups.toml.

Before

Tests.yml hand-maintained a matrix {version: ["1","lts","pre"]} × {group: ["Core","QA"]} (6 jobs) calling tests.yml@v1 directly.

After

• The matrix lives in test/test_groups.toml:

  [Core]
  versions = ["1", "lts", "pre"]
  
  [QA]
  versions = ["1", "lts", "pre"]

• Tests.yml becomes a thin caller:

  jobs:
    tests:
      uses: "SciML/.github/.github/workflows/grouped-tests.yml@v1"
      secrets: "inherit"

Why no with: inputs

• runtests.jl already dispatches on the standard GROUP env var (Core/QA) — no group-env-name override needed, and no runtests.jl change is required.
• The old job used no check-bounds, coverage, coverage-directories, or apt-packages overrides, so the thin caller carries no with: block (all defaults match the old behavior).
• Linux-only: no os field (defaults to ubuntu-latest), matching the original.

Preserved

• name: "Tests", on: triggers, and concurrency: are kept verbatim so branch-protection status checks remain valid.
• All other workflow files are untouched.

Matrix match

Ran compute_affected_sublibraries.jl . --root-matrix against the new test/test_groups.toml; it emits exactly the 6 cells the old workflow produced:

group	versions
Core	1, lts, pre
QA	1, lts, pre

All runners ubuntu-latest, continue_on_error=false (no non-fatal group like Downstream is in this root matrix — Downstream is a separate workflow). 6/6 exact match.

QA

Category A — Core/QA GROUP dispatch already existed in runtests.jl; static matrix-verification only (no local Aqua run needed). test_groups.toml parses as valid TOML and Tests.yml parses as valid YAML.

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Ignore until reviewed by @ChrisRackauckas.