feat: #88 vis inheritance + #89 pymat[...] lookup + runnable examples (3.4.0)

[gerchowl]

Summary

Unblocks build123d#1270 Materials-class adapt pass. Fixes the two bugs Bernhard reported (#88, #89) and adds a runnable cell-style example file wired into pytest.

Closes #88. Closes #89.

What's in

#88 — Grades inherit parent Vis

Before 3.4, a grade without its own [vis] TOML section had vis.source = None, forcing consumers to walk the parent chain manually. Fixed in src/pymat/loader.py — deep-copies parent._vis for grades without their own [vis], merges TOML overrides on top when present via new Vis.merge_from_toml() classmethod.

Matches the existing _add_child property-inheritance pattern. Runtime mutations stay per-material (isolated) — documented trade-off.

#89 — Exact lookup surface

• pymat["Stainless Steel 304"] — module-level subscript via PEP 562-style class swap. Matches key / name / grade (case-insensitive, NFKC + whitespace-collapse). Raises KeyError on miss (with fuzzy suggestions) or ambiguity (with candidates).
• pymat.search(q, exact=True) — list-returning exact variant. Now matches grade too (was missing — caught by falsify review).
• in operator works via __contains__.
• Non-string / empty / whitespace-only inputs raise cleanly.

Examples + test wiring

• examples/build123d_integration.py — cell-style (# %%) runnable script mirroring the pattern build123d's author uses. Covers lookup, search, inheritance, adapters, shape integration, glTF export.
• tests/test_build123d_integration_examples.py — executes the file top-to-bottom via runpy on every CI run. Any API drift breaks the example before it breaks downstream copy-paste.

Falsify review

Before implementing, the original design (deep-copy-at-access proxy for Vis) was refuted by three orthogonal reviewers:

• Python idioms: pymat.get() collides with dict.get() convention, name_or_key is a polymorphic-string smell, __getitem__ is the idiomatic shape.
• Edge cases: exact=True missing grade targets, ambiguity handling, normalization silence.
• Implementation reality: Vis.from_toml can't merge — needs an explicit merger classmethod.

Final design consolidates all three → load-time deep-copy-with-merge, __getitem__ subscript, grade-aware exact=True, full NFKC normalization.

Test plan

• 386 tests pass locally (was 329; +57 new).
• Pre-commit hooks clean (ruff format, pymarkdown, typos, etc.).
• examples/build123d_integration.py runs top-to-bottom green.
• build123d glTF export round-trip pinned (carries material through today's path).

Versioning

Minor bump 3.3.0 → 3.4.0 — additive public API, one behavior change (the #88 inheritance fix, which was surprising-but-fixing). No breaking deprecations.