refactor: new set algebra

[alexandrehoffmann]

Description

This PR implements a major refactoring of the set algebra system in samurai, replacing the old visitor-based approach with a new traverser-based architecture. The changes introduce a more modular and maintainable design for performing set operations (union, intersection, difference) on mesh cell arrays.

It also resolves a long-standing issue that resulted from the visitor-based approach that was previously implemented. This approach assumes that all sets in algebra are commutative, which is not the case. We now have a valid set algebra.

Changes:

• Complete rewrite of the subset/set algebra implementation using a traverser-based architecture
• Addition of new traverser classes for various operations (union, intersection, difference, expansion, contraction, projection, translation)
• Replacement of old visitor pattern with a cleaner set base class and traverser interface
• New utility functions for set operations and tuple/range iteration

Code of Conduct

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• I agree to follow this project's Code of Conduct

[Copilot]

Pull request overview

This PR implements a major refactoring of the set algebra system in samurai, replacing the old visitor-based approach with a new traverser-based architecture. The changes introduce a more modular and maintainable design for performing set operations (union, intersection, difference) on mesh cell arrays.

Changes:

• Complete rewrite of the subset/set algebra implementation using a traverser-based architecture
• Addition of new traverser classes for various operations (union, intersection, difference, expansion, contraction, projection, translation)
• Replacement of old visitor pattern with a cleaner set base class and traverser interface
• New utility functions for set operations and tuple/range iteration

Reviewed changes

Copilot reviewed 47 out of 47 changed files in this pull request and generated 13 comments.

Show a summary per file

File	Description
tests/test_subset.cpp	Updated tests to use new API (vmin instead of compute_min), added expand_2d, expand_3d, contract tests, contains debug code
include/samurai/subset/visitor.hpp	Deleted old visitor-based implementation
include/samurai/subset/start_end_fct.hpp	Deleted old start/end function implementation
include/samurai/subset/concepts.hpp	Deleted old concepts file
include/samurai/subset/utils.hpp	Refactored with new utility functions, contains critical bug in enumerate_items
include/samurai/subset/traversers/*.hpp	New traverser implementations for all set operations
include/samurai/subset/set_base.hpp	New base class for set operations
include/samurai/subset/nary_set_operator.hpp	New n-ary set operator implementation
include/samurai/subset/node.hpp	Simplified to include only headers
include/samurai/level_cell_array.hpp	Updated constructors to work with new set base, contains commented code
include/samurai/interval.hpp	Modified equality operator to exclude index field
include/samurai/samurai_config.hpp	Added configuration flags for new features
include/samurai/static_algorithm.hpp	Added conditional logic for native expand
include/samurai/mesh.hpp	Updated to call to_lca() on set operations
include/samurai/boundary.hpp	Added const correctness
include/samurai/algorithm.hpp	Updated for_each_interval for new API
demos/tutorial/set_operator.cpp	Updated contraction to contract function call
demos/FiniteVolume/advection_3d.cpp	New 3D advection demo

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[gouarin]

Can you check that all inline are changed by SAMURAI_INLINE ?

[gouarin]

We could also just keep the version of 'ListOfIntervals' for the traversers and delete the rest.

[alexandrehoffmann]

Can you check that all inline are changed by SAMURAI_INLINE ?

done.