public static BitBlock <BitBlock10> ToBitBlock(this BitString src, N10 n) => BitBlock.FromSpan <BitBlock10>(src.BitSeq);
public static BitBlock <BitBlock21> ToBitBlock(this BitString src, N21 n) => BitBlock.FromSpan <BitBlock21>(src.BitSeq);
public static BitBlock <BitBlock32> ToBitBlock(this BitString src, N32 n) => BitBlock.FromSpan <BitBlock32>(src.BitSeq);
public static BitBlock <T> FromSpan <T>(Span <byte> src) where T : unmanaged, IBitBlock => BitBlock <T> .FromSpan(src.Slice(0, Unsafe.SizeOf <T>()));