Function dn_equal 

pub fn dn_equal(a: &[u8], b: &[u8]) -> bool

Compare two Distinguished Name byte slices for equality, normalising the SET/SET-OF structure.

X.509 DNs can encode the same logical set of attributes with different SET granularity (e.g. a single SET with two attributes vs two SETs with one attribute each). This function flattens both DNs into a list of (OID, value) pairs, sorts them, and compares the sorted lists.

Returns true if the DNs are semantically equal.