fix(ci): use explicit features for rustdoc build

--all-features enables ilp-scip which requires SCIP solver not
available in CI. Use --features ilp-highs to match the CI workflow.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: GiggleLiu

.github/workflows/docs.yml

@@ -45,7 +45,7 @@ jobs:
         run: make examples && typst compile --root docs docs/paper/reductions.typ book/reductions.pdf
 
       - name: Build rustdoc
-        run: RUSTDOCFLAGS="--default-theme=dark" cargo doc --all-features --no-deps
+        run: RUSTDOCFLAGS="--default-theme=dark" cargo doc --features ilp-highs --no-deps
 
       - name: Combine documentation
         run: |