Pass only retained nodes to MueLu

[amgebauer]

Filtering eliminated nodes before passing them to MueLu. Eliminated nodes occur in periodic boundary conditions.

On the way, I had to fix some consts to make it possible.

Closes #1634

Part of #1600

[Copilot]

Pull request overview

This pull request filters eliminated nodes (slave nodes in periodic boundary conditions) before passing node coordinates to the MueLu solver. The main change introduces a new function extract_retained_node_coordinates that creates a filtered node map excluding PBC slave nodes. Additionally, the PR adds const correctness to various PBC-related functions and methods throughout the codebase.

• Introduces extract_retained_node_coordinates to filter out PBC slave nodes before passing to MueLu
• Adds const correctness to PBC-related getters and iterators
• Updates map access patterns from operator[] to at() for const maps

Reviewed changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/core/fem/src/discretization/4C_fem_discretization_utils.cpp	Implements new extract_retained_node_coordinates function that filters PBC slave nodes
src/core/fem/src/discretization/4C_fem_discretization_utils.hpp	Declares the new extract_retained_node_coordinates function
src/sti/4C_sti_monolithic.cpp	Replaces extract_node_coordinates with extract_retained_node_coordinates
src/scatra/4C_scatra_timint_meshtying_strategy_s2i.cpp	Replaces extract_node_coordinates with extract_retained_node_coordinates, but has incomplete type declaration
src/scatra/4C_scatra_timint_implicit_service.cpp	Replaces extract_node_coordinates with extract_retained_node_coordinates
src/core/linear_solver/src/method/4C_linear_solver_method_parameters.cpp	Replaces extract_node_coordinates with extract_retained_node_coordinates
src/core/fem/src/discretization/4C_fem_discretization.hpp	Adds const qualifiers to PBC-related getter methods
src/core/fem/src/discretization/4C_fem_discretization.cpp	Implements const versions of PBC getter methods
src/core/fem/src/discretization/4C_fem_discretization_faces.cpp	Updates to use const PBC maps and replaces operator[] with at()
src/core/fem/src/discretization/4C_fem_discretization_partition.cpp	Adds const qualifier to PBC map pointer
src/core/fem/src/dofset/4C_fem_dofset_pbc.hpp	Adds const qualifiers and [[nodiscard]] to getter methods
src/fluid_ele/4C_fluid_ele.hpp	Adds const qualifier to PBC connectivity parameter
src/fluid_ele/4C_fluid_ele_intfaces.cpp	Updates to use const auto for PBC iterators
src/fluid_ele/4C_fluid_ele_intfaces_calc.cpp	Adds const qualifier to PBC connectivity pointer
src/fluid_turbulence/4C_fluid_turbulence_boxfilter.cpp	Adds const qualifiers to PBC map pointers
src/core/fem/src/general/utils/4C_fem_general_utils_superconvergent_patch_recovery.cpp	Adds const qualifiers and uses auto for PBC iterators
src/core/fem/src/general/utils/4C_fem_general_l2_projection.cpp	Adds const qualifier to PBC map pointer

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[maxfirmbach]

LGTM!