Rebalance

[helloworld922]

Various small changes to Laghos:

• Fixed building if mfem is installed in a symlink'd folder
• Added optional user.mk file for user build config
• Added option to force non-conforming meshes (in 2D and 3D)
• Added option to rebalance mesh after parallel refinement
• Ensure timing sections measure GPU kernel execution correctly
• Fixed some integer overflow problems with FOM calculations

[Copilot]

Pull Request Overview

This PR introduces several small changes to Laghos aimed at improving build flexibility, GPU kernel timing accuracy, and mesh handling. Key changes include:

• Inclusion of an optional user.mk file in the makefile and enhanced MFEM directory resolution.
• Updates to use HYPRE_BigInt types for global sizes in laghos_solver.hpp and laghos.cpp to fix integer overflow issues.
• Addition of GPU device synchronization (LAGHOS_DEVICE_SYNC) calls in laghos_solver.cpp and new command-line options in laghos.cpp to enable non-conforming meshes and mesh rebalancing.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

File	Description
makefile	Added inclusion of user.mk and refined MFEM directory comparisons.
laghos_solver.hpp	Updated global true vector size types from HYPRE_Int to HYPRE_BigInt.
laghos_solver.cpp	Inserted LAGHOS_DEVICE_SYNC calls around GPU kernel launches and timing sections.
laghos.cpp	Introduced options for non-conforming meshes and mesh rebalancing; updated types.