[kosha] Explore different bitfield orderings

[akprasad]

In packing, I chose a bitfield ordering more or less on a hunch, but I don't think our current ordering works very well because our modular_bitfield crate uses an endianness that's different from what I expected.

I think a better ordering or approach here could potentially decrease the size of the FST. My guess is that we might save up to 10% on size, which means more of the FST can be kept in the processor cache.

A good PR here should quantify the size decrease when using a different bitfield ordering.