Restrict Vanka patches to the adaptively refined region

[pbrubeck]

Depends on PETSc petsc/petsc!9484, the tip of the stack !9480 → !9414 → !9481 → !9484. The last commit points CI at that branch and must be dropped before merging.

ASMVankaPC built its index sets in Python, taking each seed's star and closure through getTransitiveClosure and gathering the dofs point by point — the same general path ASMStarPC had before #5329. Coloring already grouped ASMStarPC's patches and restricted them to an adaptively refined region, but ASMVankaPC had neither: every entity of the stratum got a patch, so a smoother on an adaptively refined level relaxed the whole mesh to fix a corner of it, and -pc_vanka_use_coloring had no restriction to key its grouping on.

ASMVankaPC now shares ASMStarPC's Cython IS-construction mechanism in firedrake/cython/patchimpl.pyx. create_star_points() takes the star of each owned seed as before; the new create_closure_points() takes the closure of a group of points, which applied to those stars is what -pc_patch_construct_type vanka solves for. Seeds may be restricted to the region that was genuinely refined, the same way ASMStarPC's do, and the coloring then colors only those.

Changes

• create_closure_points() and the widened create_patch_ises() replace build_vanka_indices()/get_entity_dofs(), which are gone. create_patch_ises() now takes points and offsets per subspace rather than one array shared by all of them, since a Vanka patch's excluded subspaces (pc_vanka_exclude_subspaces) read only the star — or, with pc_vanka_include_type entity, the seed alone — while the included ones read its closure.
• get_colors() no longer forces mat_coloring_type to power for the distance-three separation Vanka patches need: PETSc's DMPlexCreateColoringLabel() (petsc/petsc!9484) now folds the requested distance into the graph it colors, so the default greedy coloring, applied at distance one, is correct for any distance.
• pc_vanka_construct_label/_value and pc_vanka_adaptive restrict ASMVankaPC the same way the equivalent ASMStarPC options do. PatchPC already applies the same restriction for -patch_pc_patch_construct_type vanka, since its adaptive option is construct-type agnostic.

Options

Option	Effect
pc_vanka_adaptive	Restricts ASMVankaPC to the entities whose patch meets the refined region, building the label from mesh.adaptive_cell_maps.
pc_vanka_construct_label / _value	Restricts ASMVankaPC to any DMLabel already on the mesh's DMPlex, for a region the adaptive machinery did not produce.
pc_vanka_use_coloring	Unchanged in meaning, but now also colors only the selected entities when combined with either of the above, and correctly separates patches at Vanka's wider reach while respecting pc_vanka_exclude_subspaces.

Tests

Added to tests/firedrake/regression/test_star_pc.py: test_adaptive_vanka_equivalence, test_adaptive_vanka_coloring, and test_adaptive_vanka_is_restricted, mirroring the existing test_adaptive_star_* tests but driving a manufactured Taylor-Hood Stokes problem through ASMVankaPC and PatchPC(construct_type=vanka). They run at 1 and 3 processes; the latter needs mesh overlap distance two rather than one, since a Vanka patch reaches further than a star patch, so a new adaptive_vanka_mesh fixture supplies it alongside the existing adaptive_mesh.

AI was used to draft this change (Claude Code, Sonnet 5).