Type of the non-final entries of an Array `.value` when precision is applied in constructor

Splitting off from #141 , where the suggestion was that if fractionDigits is supplied as an option in the constructor, we need to make a decision about the types of the entries in the store .value array, in particular the non-final ones. Example:

let a = new Amount([5, 11.1], { unit: "foot-and-inch", fractionDigits: 0 })

Should a.value be [5, "1.1e+1"] or ["5e+0", "1.1e+1"]?

Storing only the last entry as a decimal-digit string matches the rule that an input numeric value gets stringified when precision is applied to it. The earlier entries are required* to be integers, so they carry no precision information. Following the "stop coercing things" philosophy, an input Number stays a Number. The result is the mixed array [5, "1.1e+1"].

(* This argument assumes that the only units we support in sequence units are always integer multiples of one another, starting from the smallest to the biggest. That should be safe to assume but perhaps there are counterexamples.)

On the other hand, the "precision specified --> stringify" principle could be understood as applying to each component of the argument, even if it requires us to put an integral Number in quotes. Moreover, there may be something to be said for favoring uniform arrays. Thus, we ought to store ["5e+0", "1.1e+1"].

We need to decide which principles we want to stick to in the context of sequence units and make a decision. Presumably the same logic ought to apply to .convertTo, too.

Read the discussion in #141 and compare the constructor's precision behavior with the proposed .value representations for sequence units. Then examine how .convertTo should follow the same rule. Done means the project has decided and documented whether non-final entries remain Numbers or are stringified.