f128_internal - license material provenance

Declared license: MIT (Cargo.toml of each sub-crate).
Author: Joshua Karns. Source archive: sources/f128-7f971c34568dd6ae4e97a602bf15c23137b2cad5.tar.gz
(jkarns275/f128 @ 7f971c34). The upstream archive ships no LICENSE file; the
text below is the canonical MIT text, added so the distribution carries usable
text matching the declared license. Marked declared-only, not upstream-collected.
