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

All PRs are reviewed by the PhysicsNeMo team before merging.

Depending on which files are changed, GitHub may automatically assign a maintainer for review.

We are also testing AI-based code review tools (e.g., Greptile), which may add automated comments with a confidence score.
This score reflects the AI’s assessment of merge readiness and is not a qualitative judgment of your work, nor is
it an indication that the PR will be accepted / rejected.

AI-generated feedback should be reviewed critically for usefulness.
You are not required to respond to every AI comment, but they are intended to help both authors and reviewers.
Please react to Greptile comments with 👍 or 👎 to provide feedback on their accuracy.

[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