Pull in refactor from old branch.

[kbonney]

Summary

Cleans up core abstractions in src/pynumad/objects/, improves separation of concerns, eliminates dead code, and replaces parallel array structures with pandas.DataFrame.

Structural / design changes

• Blade.ispan is now a @property delegating to definition.ispan, eliminating the need to keep two copies in sync
• BillOfMaterials and MaterialDatabase no longer inherit from dict; both are plain classes with typed attributes
• BladeSettings collapsed into Blade (mesh_size: float = 0.45); settings.py deleted
• Stack / Ply moved to a new objects/stack.py module; Layer moved from materialdb.py to material.py
• KEY_LABELS extracted as a module-level constant in keypoints.py and imported by component.py
• ispan consolidated to Definition: Removed self.ispan from Geometry entirely. Geometry.generate() now uses a local variable, update_oml_geometry() receives span location as an explicit transZ parameter, and all external callers (KeyPoints, BillOfMaterials, analysis modules) read directly from blade.definition.ispan.

Data model changes

• Definition parallel ndarray attributes (chord, degreestwist, leband, sparcapwidth_hp, etc.) replaced by two pd.DataFrame objects — span_data (indexed by span location) and ispan_data (indexed by ispan location); original attribute names remain as properties for backward compatibility
• BillOfMaterials hp/lp/sw changed from lists of BillOfMaterialsEntry objects to pd.DataFrame; the separate indices dict is removed and its contents are now columns within the same DataFrames; sw consolidates from a list-of-lists to a single DataFrame with a web_id column
• MaterialDatabaseEntry converted to a @dataclass

Code quality

• Material, BillOfMaterialsEntry (now removed), Ply, Layer, and Station converted to @dataclass
• rotate2d moved to utils/affinetrans.py; airfoil utility functions made private (_ prefix); dead _adjust_te deleted
• Component._compare() and redundant _compare() on Layer removed in favor of __eq__
• Dead code removed: ShearWeb class, MATLAB-remnant comment blocks, unreachable swRegion branch, commented-out Station property stubs
• KeyPoints.generate() no longer mutates definition.leband/definition.teband
• Geometry config flags (_natural_offset, _rotorspin, _swtwisted) initialized to None in __init__ rather than hardcoded defaults
• BillOfMaterials.generate() explicit inputs: Signature changed from generate(definition, keypoints) to generate(ispan, components, materials, keypoints), naming its actual dependencies rather than accepting the entire Definition object.

Bug fixes

• Blade.__init__ file-reading block was misplaced inside ispan.setter; moved back to __init__
• keypoints.py web_areas scalar assignment failed when np.dot returned a 1-element array instead of a scalar; fixed with np.squeeze + float()
• Definition.span / ispan setters now always recreate the DataFrame on assignment, fixing a pandas length-mismatch error triggered by the Excel reader's double-assignment pattern

Tests and documentation

Tests still pass after the refactor!

Acknowledgement

By contributing to this software project, I acknowledge that I have reviewed the software quality assurance guidelines and that my contributions are submitted under the Revised BSD License.