F05-NEW-AF-01: fix panic on signed precision values in enum_val_to_ord

[dcorral]

enum_val_to_ord read GS_PRECISION by calling unwrap_uint on any StrictVal::Number, which panics on a signed or negative value instead of returning None.

The match now takes only StrictNum::Uint. Every other numeric variant falls through to the existing _ => None, the same path an unrecognised enum variant already takes.

No signature change: the function already returns Option<u8>.