feat: adding rkyv export support and convert back to native type

[samuelgja]

feat: add rkyv export support and convert back to native type

Summary

Add rkyv-gated helpers to convert archived half-precision types back to their native counterparts, and re-export the archived types from the crate root.

Changes

• src/bfloat.rs

  • Under #[cfg(feature = "rkyv")], implement impl Archivedbf16:
    • Add pub fn to_native(&self) -> bf16 to convert the archived value back to bf16.

• src/binary16.rs

  • Under #[cfg(feature = "rkyv")], implement impl Archivedf16:
    • Add pub fn to_native(&self) -> f16 to convert the archived value back to f16.

• src/lib.rs

  • Under #[cfg(feature = "rkyv")]:
    • Re-export bfloat::Archivedbf16.
    • Re-export binary16::Archivedf16.

Motivation

These helpers make it easier to round-trip bf16/f16 when using rkyv, and the root re-exports improve ergonomics by exposing the archived types alongside their native counterparts.