Add `f16b` type to core::num

// The `f16b` type is not yet available in Rust 1.99.0 (edition 2024).
// We demonstrate the problem it solves by using a `u16` as a stand‑in
// for a 16‑bit floating‑point value and converting to `f32` for math.

fn main() {
    // Imagine this `u16` holds the raw bits of an `f16b` value.
    let raw: u16 = 0b0011_1100_0000_0000; // example bit pattern

    // Convert the raw bits to `f32` using a manual conversion.
    // In real code this would be `f32::from(f16b::from_bits(raw))`.
    let f: f32 = f32::from_bits((raw as u32) << 16);

    // Perform some arithmetic on the `f32`.
    let result = f * 2.0 + 1.0;

    // Convert back to the 16‑bit representation (truncating the mantissa).
    let raw_result = (result.to_bits() >> 16) as u16;

    println!("Original bits: {:#06x}", raw);
    println!("As f32: {}", f);
    println!("Result as f32: {}", result);
    println!("Result bits (as f16b placeholder): {:#06x}", raw_result);
}