feat(data): add borated PE, ordinary concrete, SF6 (#144, #145, #146)

[gerchowl]

Summary

Phase 5 batch 9 — three shielding / dielectric materials closing the final issues in the Materials Catalog Expansion milestone (29 entries total).

Key	Where	Density (g/cm³)	Headline scalar	Primary source
borated_pe	plastics.toml	0.955	tensile 27.6 MPa, HDT 77 °C, flexural modulus 1.38 GPa	Emco Plastics 5 wt% B borated HDPE TDS (vendor)
concrete_ordinary	ceramics.toml	2.30	X₀ = 11.55 cm, λ = 42.39 cm, I = 135.2 eV, Z_eff = 11	NIST PML PSTAR matno=144 (PD-USGov) + PDG 2024 shielding-concrete (CC-BY-4.0)
sf6	gases.toml	6.16 × 10⁻³	k = 13.45 mW/(m·K), Cp = 664 J/(kg·K), V_bd = 8.9 kV/mm, ε_r = 1.002	Guder & Wagner 2009 EOS, Assael 2012 JPCRD (NIST PD-USGov), Christophorou-Olthoff-Van Brunt 1997 NIST (PD-USGov), JANAF Chase 1998 (PD-USGov), Kita 1994 (paywalled)

Closes #144, #145, #146.

Hazard / caveats

• SF6 GWP ≈ 23,500 — noted in a header comment; no schema field for GWP.
• SF6 sublimates at 1 atm (sublimation point 209.3 K); melting_point stores the triple-point T (223.7 K = -49.5 °C). Sublimation point documented in _sources.note since the schema lacks a sublimation field.
• Borated PE nuclear table intentionally omitted — PDG does not list borated PE separately, and the (n,α) capture cross-section has no schema slot. # TODO: schema neutron_capture_xs documents the gap. Z_eff and X₀ for unborated PE differ by ≪ 5 % from the borated value, so users requiring nuclear scalars can use pe.hdpe as a fallback.
• Ordinary concrete mechanical / thermal scalars (E, f'c, k, Cp, CTE) omitted — they vary by ~3× with mix design, w/c ratio, age, and moisture content, and we have no single primary government reference that pins them to the Portland-concrete composition. ACI 318 / fib MC2010 are the downstream references.

Files

• src/pymat/data/plastics.toml — borated_pe block + per-property _sources (vendor, proprietary-reference-only)
• src/pymat/data/ceramics.toml — concrete_ordinary block + per-property _sources (PD-USGov + CC-BY-4.0)
• src/pymat/data/gases.toml — sf6 block + per-property _sources (PD-USGov for Assael/Christophorou/JANAF, proprietary-reference-only for Guder-Wagner / Kita)
• src/pymat/__init__.py — _CATEGORY_BASES updated for borated_pe, concrete_ordinary, sf6
• LICENSES-DATA.md — regenerated; PDG 2024 shielding-concrete entry added (CC-BY-4.0)

Test plan

• python -c "import tomllib; tomllib.loads(open('src/pymat/data/plastics.toml').read())" — valid TOML
• python -c "import tomllib; tomllib.loads(open('src/pymat/data/ceramics.toml').read())" — valid TOML
• python -c "import tomllib; tomllib.loads(open('src/pymat/data/gases.toml').read())" — valid TOML
• python scripts/check_licenses.py — passes (7 TOMLs scanned)
• uv run pytest tests/test_toml_integrity.py tests/test_sources.py -v — 43 / 43 pass
• uv run pytest — 628 passed, 24 skipped (visual-regression)
• uv run ruff check . && uv run ruff format --check . — clean
• uv run python -c "from pymat import borated_pe, concrete_ordinary, sf6; print(borated_pe.density, concrete_ordinary.density, sf6.density)" → 0.955 2.3 0.00616