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This patch introduces a new algorithm for multiplication of tristate
numbers (tnums) that is provably sound. It is faster and more precise when
compared to the existing method.

Like the existing method, this new algorithm follows the long
multiplication algorithm. The idea is to generate partial products by
multiplying each bit in the multiplier (tnum a) with the multiplicand
(tnum b), and adding the partial products after appropriately bit-shifting
them. The new algorithm, however, uses just a single loop over the bits of
the multiplier (tnum a) and accumulates only the uncertain components of
the multiplicand (tnum b) into a mask-only tnum. The following paper
explains the algorithm in more detail: https://arxiv.org/abs/2105.05398.

A natural way to construct the tnum product is by performing a tnum
addition on all the partial products. This algorithm presents another
method of doing this: decompose each partial product into tw...