Add AdvancedMDBC boundary mode with improved ghost-cell corrections

[AhmedSalih3d]

Motivation

• Introduce a richer MDBC boundary treatment that performs extra numerical checks, reconstructs ghost pressures/densities, and enforces a no-slip-like velocity correction while preserving the existing SimpleMDBC path.

Description

• Add a new AdvancedMDBC subtype of MDBCMode and export it from SimulationMetaDataConfiguration and SPHExample so it can be selected via the SimulationMetaData type parameter.
• Provide LoadMDBCNormals! overload for AdvancedMDBC in PreProcess.jl to load ghost points and normals just like SimpleMDBC.
• Implement ComputeInteractionsMDBCAdvanced!, NeighborLoopMDBCAdvanced!, and ApplyMDBCCorrectionAdvanced in src/SPHCellList.jl to accumulate per-ghost matrices/vectors, run numerical checks (determinant/condition thresholds), perform matrix solves or fallback density estimates, clone/adjust pressure with hydrostatic correction, and reflect velocities for a no-slip treatment when sufficient kernel coverage exists.
• Wire the advanced MDBC flow into the symplectic predictor/corrector path by calling ApplyMDBCBeforeHalf! for AdvancedMDBC before the full time-step (while leaving SimpleMDBC and NoMDBC behavior intact) and document the new option in README.md.

Testing

• No automated tests were run on these changes.

---

Codex Task