feat: refactor partitioners

[bd713]

Description

This PR introduces a complete refactoring of GEOS's mesh partitioning system with a new architecture that separates partitioning algorithms (engines) from domain decomposition strategies (partitioners).

In practice, a new DomainPartitioner abstract base class is introduced with two main specialized branches:

DomainPartitioner (Abstract Base)
├── GeometricPartitioner (Abstract)
│   ├── CartesianPartitioner (Concrete)
│   └── ParticleCartesianPartitioner (Concrete)
└── MeshPartitioner (Abstract)
    ├── CellGraphPartitioner (Concrete)
    └── LayeredMeshPartitioner (Concrete)

The mesh partitioners leverage low-level graph partitioner engines that are independent from MPI communication:

GraphPartitionEngine (Abstract Engine Interface)
├── ParMetisEngine (Concrete)
├── PTScotchEngine (Concrete)
└── NoOpEngine (Concrete)

A PartitionerManager is introduced for creating and managing partitioner instances.

XML Changes

Partitioning configuration moved from mesh-embedded to dedicated <Partitioner> section.

Before:

<Mesh>
   <VTKMesh
       file="mesh.vtu"
       partitionMethod="parmetis"
       partitionRefinement="2"  />
</Mesh>       

After:

<Partitioner>
  <CellGraphPartitioner engine="parmetis" numRefinements="1"/>
</Partitioner>
<Mesh>
  <VTKMesh file="mesh.vtu"/>
</Mesh>

Default behavior
If no partitioner is prescribed, an appropriate default is selected based on mesh type:

• Internal meshes: CartesianPartitioner
• External meshes: CellGraphPartitioner with ParMetis

To skip graph partition optimization, explicitly use engine="noop".

Testing & Rebaseline

Due to XML schema changes a rebaseline is required.
However no numerical impact is expected.

INFO: Total number of log files processed: 1047

INFO: No unfiltered differences were found.

All currently failing integrated tests are due to structural changes such as:

********************************************************************************
Error: /Problem
	Group has a child 'Partitioner' in the file to compare but not the baseline file.
********************************************************************************
********************************************************************************
Error: /Problem/domain
	Group has a child 'partitionManager' in the baseline file but not the file to compare.
********************************************************************************