Function pack_version 

pub const fn pack_version(major: u8, minor: u8, patch: u8) -> u16

Pack a semantic version into a u16 using 5.5.6 encoding.

Layout: (major << 11) | (minor << 6) | patch

• major: 0–31, minor: 0–31, patch: 0–63
• 0xFFFF is reserved as “no version” (erased flash sentinel).