Adds DomainMesh improvements, docs, and bugfixes

[peterdsharpe]

PhysicsNeMo Pull Request

Description

Contains a bunch of small improvements to DomainMesh, such as:

• Adding DomainMesh.draw() to mirror Mesh.draw() with multi-mesh support.
• Allows multi-mesh plotting capabilities with PyVista visualization backend.
• Fixes a bug in DomainMesh.n_boundaries, where we were incorrectly returning the `TensorDict
• DomainMesh.check_boundary_watertight() bugfix by deduplicating vertices before watertightness check

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.
• The CHANGELOG.md is up to date with these changes.
• An issue is linked to this pull request.
• If I am implementing a new model or modifying any existing model, I have followed the Models Implementation Coding Standards.

Dependencies

Review Process

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[greptile-apps]

Greptile Summary

This PR adds DomainMesh.draw() for multi-mesh visualization (with PyVista overlay support), correctly fixes n_boundaries (was returning a TensorDict instead of an int), and fixes is_boundary_watertight() by calling .clean() before the watertightness check to deduplicate shared vertices across independently-meshed patches. It also exports find_nearest_cells and match_points from the sampling __init__.py, and ships a comprehensive test suite for DomainMesh transforms. The one minor inconsistency is that show_edges is forwarded to the interior draw but not to boundary draws in DomainMesh.draw().

Important Files Changed

Filename	Overview
physicsnemo/mesh/domain_mesh.py	Adds DomainMesh.draw(), fixes n_boundaries (was returning TensorDict), and fixes is_boundary_watertight() with .clean() dedup; one minor inconsistency with show_edges not forwarded to boundary draws.
physicsnemo/mesh/visualization/_pyvista_impl.py	Adds plotter parameter to draw_mesh_pyvista to enable multi-mesh overlay on a shared PyVista Plotter; the module-level pv import is safe since this module is only imported lazily after pyvista availability is confirmed.
physicsnemo/mesh/visualization/draw_mesh.py	No functional changes visible; forwards plotter via ax parameter to pyvista backend, enabling DomainMesh.draw() overlay pattern.
physicsnemo/mesh/sampling/init.py	Adds find_nearest_cells and match_points to public exports; both functions were already implemented in sample_data.py.
test/mesh/test_domain_mesh_transforms.py	Comprehensive new test file covering apply, translate, rotate, scale, transform, clean, strip_caches, subdivide, data operations, validation, chaining, and domain-level global_data transformation.

_{Reviews (1): Last reviewed commit: "formatting" | Re-trigger Greptile}

[peterdsharpe]

/blossom-ci

[coreyjadams]

Really nice notebook! The rest of the pr is great, pretty self explanatory. I have one small question I noticed but I suspect it's easy.

DomainMesh is really a killer app in the new release!

[peterdsharpe]

/blossom-ci