Fix test suite for OCC 7.9 / Python 3.14; add CI, docs, examples & lint toolchain

[LayerDynamics]

Summary

Brings PyOCC to a green, lint-clean state on the current conda-forge stack
(pythonocc-core 7.9.3, NumPy 2, Python 3.14) and stands up the project
tooling that was previously empty (CI, license, contributing guide, docs,
examples, markdown lint).

Starting point: the suite couldn't even be collected (a repo-root __init__.py
shadowed the installed package), and once collectable it was 59 failed + 1
collection error. End state: 275 passed, 19 skipped, 0 failed, with
ruff + black + pymarkdown all clean.

Core / runtime fixes

• Shape hierarchy: reparent Vertex/Edge/Wire/Shell/Solid/Compound under
  Shape, pruning the mixins Shape already provides to avoid C3 MRO errors;
  shape.py imports the concrete wrappers lazily to break the import cycle.
• OCC 7.x API drift: rewrite get_triangles() to the 7.6+ triangulation API
  (BRep_Tool.Triangulation + NbNodes/Node/NbTriangles/Triangle().Get()); the
  pyocc_shape()/create_from_topods() factory now down-casts to the concrete
  TopoDS_* type so load_stl/load_brep and topology explorers wrap correctly.
• Unified find_closest_point_data() to the (point, middle, distance)
  3-tuple contract every caller already indexed.
• Bug fixes: Edge.point() raw-parameter branch (Interval.a/.b),
  DisplayMaterial mutable-numpy dataclass defaults (default_factory), an
  undefined Shell reference in Solid.make_from_shell, de-duplication in
  vertices_from_face/edges_from_vertex, and wires_from_face double-wrapping.
• API completeness: boolean ops are now instance methods (a.union(b) and
  Solid.union(a, b)); OffscreenRenderer(width=, height=); the missing
  MultiViewRenderer/BatchProcessor/viewer methods are implemented; the
  _process_single_shape stub data is replaced with real analysis/exports.
• New: UniformGrid + sample_face_uniformly/sample_edge_uniformly;
  2D uv_bounds + Box.__iter__; arc-length finder precision.

Tests

275 passed, 19 skipped, 0 failed. The 19 skips are the OpenGL offscreen
viewer/render tests — they need a display, so CI runs them under Xvfb.
Added io_test.py (STEP/STL/BREP round-trips, previously untested) and an
Edge.point() raw-parameter regression test.

Tooling / docs

• CI workflows (check.yml, build.yml, publish.yml): micromamba env;
  ruff + black + pymarkdown gates; pytest under Xvfb; sdist/wheel build +
  conda smoke-import; PyPI trusted publishing on release.
• Lint to zero: cleared all ruff issues; switched import sorting to ruff's
  black-compatible isort (the standalone isort oscillated with black); added
  PyMarkdown + a shared .markdownlint.jsonc config; fixed pyproject URLs.
• Docs: LICENSE, CONTRIBUTING.md, docs/ (architecture, developer guide,
  API reference), and runnable examples/. Removed the dead repo-root
  __init__.py shim.

Notes for review

• The OpenCASCADE offscreen-render paths are CI-verified-only (they can't run
  without a GL display, so they're exercised under Xvfb in CI rather than locally).
• CLAUDE.md is intentionally gitignored and not included.

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