feat(mesh): add Nastran conversion with result preservation

[mnabian]

Description

Add NastranSource and MeshVTKSink to convert Nastran deck/OP2 datasets into native .pmsh, VTU, legacy VTK, or boundary VTP.

• Discover result fields dynamically, align unambiguous nodal/element tables by ID, and retain other layouts as raw tables.
• Preserve original connectivity, cards, constraints, and input bytes for exact recovery. VTU/VTK retain quadratic cells; native meshes use linear projections.
• Support sparse/complex results, nested metadata, and guarded export after mesh transformations.

Support depends on pyNastran and supported element topologies. Embedded originals increase storage and can be disabled. VTP displays boundary fields while retaining the global archive. No customer data is included.

Validation

• 155 feature tests passed with 96.5% statement coverage; generic VTK tests also pass with NumPy 2.
• Both local sample datasets round-trip exactly through all four formats; source files recover byte-for-byte.
• Strict Sphinx and changed-file pre-commit checks pass. Existing unrelated Rust CI and repository-wide Markdown failures are documented.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.
• An issue is linked to this pull request.

Dependencies

pyproject.toml and uv.lock are unchanged from the base branch. Install the optional reader explicitly with pip install 'physicsnemo-curator[mesh]' 'pyNastran>=1.4.1,<1.5'. CI uses invocation-only reader dependencies through uv run --with; existing dependency declarations and default environments remain unchanged.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.21560% with 33 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.71%. Comparing base (4111fce) to head (bf348d2).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...o_curator/domains/mesh/sources/_nastran_results.py	93.49%	11 Missing ⚠️
..._curator/domains/mesh/sources/_nastran_geometry.py	94.65%	7 Missing ⚠️
...physicsnemo_curator/domains/mesh/sinks/mesh_vtk.py	97.60%	6 Missing ⚠️
...physicsnemo_curator/domains/mesh/sinks/__init__.py	25.00%	3 Missing ⚠️
..._curator/domains/mesh/sources/_nastran_metadata.py	97.41%	3 Missing ⚠️
...hysicsnemo_curator/domains/mesh/sources/nastran.py	98.47%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #67      +/-   ##
==========================================
+ Coverage   63.39%   65.71%   +2.31%     
==========================================
  Files          88       93       +5     
  Lines        9488    10359     +871     
==========================================
+ Hits         6015     6807     +792     
- Misses       3473     3552      +79     

Flag	Coverage Δ
integration	65.71% <96.21%> (+2.31%)	⬆️
unit	65.71% <96.21%> (+2.31%)	⬆️

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