Constant ACCENT_MARKER_MASK 

const ACCENT_MARKER_MASK: u128 = _; // 85_070_591_868_883_900_266_094_632_177_103_798_272u128

128-bit bitmap of ACCENT_MARKERS for branchless ASCII membership testing. Bit n is 1 iff byte n is an accent marker. Computed at compile time from ACCENT_MARKERS so the two stay in lockstep.