Some seeds come coated in stuff. I think that's just to make them visually easier to distinguish between other seeds made other colors in the same packet, but I could be wrong. It might extend the life of the seed.
One seed store I shopped at once vaccuum packed its seeds for extended shelf-life.
The ancients (or people hundreds and/or thousands of years ago) sometimes put seeds in clay balls in caves. People discovered some of those and found they were still viable after a super long time. Maybe perfect the art of making clay balls!
It's probably very doable. Having your own cave might be a little harder, but we don't know if the cave is necessary. Maybe use a root cellar, or just put them wherever. I imagine the clay insulates well.
They put other things in clay balls besides seeds, though (e.g. some valuables; perhaps jewelry).