ci: uniformize onto centralized CI (project-model SublibraryCI + cleanup) (SciML#1216)

* ci(SublibraryCI): use centralized project-model workflow

Replace the GROUP-dispatch sublibrary-tests.yml call (the root runtests.jl
does not map GROUP to a sublibrary, so lib/* were not actually tested) with
the centralized project-model sublibrary-project-tests.yml: list lib/* and
test each via tests.yml project=lib/X.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* ci: uniformize — rm-CompatHelper add-DocPreviewCleanup

Part of bringing this repo onto the full centralized CI setup (SciML/.github
@v1): remove retired CompatHelper (Dependabot drives [compat]) and/or add the
centralized Documenter preview cleanup.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: ChrisRackauckas-Claude <accounts@chrisrackauckas.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 3 people

.github/workflows/CompatHelper.yml

@@ -0,0 +1,17 @@
+name: Doc Preview Cleanup
+
+on:
+  pull_request:
+    types: [closed]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: write
+
+jobs:
+  doc-preview-cleanup:
+    uses: "SciML/.github/.github/workflows/docs-preview-cleanup.yml@v1"
+    secrets: "inherit"

.github/workflows/DocPreviewCleanup.yml

@@ -1,19 +1,22 @@
 name: Sublibrary CI
+
 on:
   pull_request:
     branches:
       - master
     paths-ignore:
-      - "docs/**"
+      - 'docs/**'
   push:
     branches:
       - master
     paths-ignore:
-      - "docs/**"
+      - 'docs/**'
+
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: ${{ startsWith(github.ref, 'refs/pull/') }}
+
 jobs:
-  sublibrary-ci:
-    uses: "SciML/.github/.github/workflows/sublibrary-tests.yml@v1"
+  sublibraries:
+    uses: "SciML/.github/.github/workflows/sublibrary-project-tests.yml@v1"
     secrets: "inherit"