Integrate NIST Cryogenic Materials Property Database — low-T data

[gerchowl]

Free public-access database with polynomial fits for metals + structural plastics (G10, Kapton, PTFE, etc.) at 4–300 K. US-gov public domain.

Unique value: only authoritative source for low-T thermal conductivity, specific heat, and integrated thermal conductivity for cryogenic detector work (LYSO/SiPM cooling, LN2 dewars, LHe). Directly feeds the T-curve schema (#148).

Action: parse polynomial coefficients into <prop>_curve entries for: aluminum (6061-T6, 1100), copper (OFHC), stainless 304/316, Ti-6Al-4V, Invar, brass, lead, beryllium, G10, Kapton, PTFE.

Reference: https://trc.nist.gov/cryogenics/materials/materialproperties.htm

[gerchowl]

Deferred to a future 4.x minor release per Phase 4 design review (3 parallel reviewers, May 2026). NIST Cryogenic Materials Database — deferred to 4.x: low-T data is a niche use case with zero current-consumer signal (build123d doesn't care about cryogenic property variations). Schema infra (T-curves from #148) is in place; populates whenever a cryo consumer materializes.

Not closed — the issue stays open with the deferred-4.x label so it surfaces in future planning.