Function thermal_zone 

pub fn thermal_zone(
    type_text: Option<&str>,
    temp_text: &str,
) -> Option<ThermalZone>

2026-09-26: Assemble one zone from its type and temp file contents.

A zone whose temperature does not parse is dropped: an unreadable zone is not a 0 °C zone, and the hottest zone feeds the precheck and the equivalence test.