Simplify a product of numbers that cancels to one

[dqnykamp]

Simplifying a numeric matrix subtraction such as

me.fromAst(["+", A, B, ["-", C]]).simplify();

either produced a wrong entry or threw TypeError: Cannot read properties of undefined (reading '0'), depending on the numbers involved.

Cause

simplify_integers_in_roots merges the factors of a product, collecting numeric factors into numberFactor and everything else into otherFactors. It then omits numberFactor from the result when it equals one:

if (numberFactor !== 1) {
  otherFactors.unshift(numberFactor);
}

return ["*", ...otherFactors];

When the product consisted entirely of numbers, otherFactors is empty, so a product whose numbers cancel to one became the empty multiplication ["*"], which evaluate_numbers_sub reduces to undefined.

Ordinary numeric products never reach that state, because simplify evaluates numbers before this pass runs. The products created by distributing a scalar over a vector, tuple, or matrix do, since perform_vector_matrix_additions_scalar_multiplications builds them afterwards. An entry whose product with the scalar is one — most commonly an entry of -1 in a matrix being subtracted — therefore vanished from the entry's sum. What the reader saw depended on how default_order sorted the broken node among the remaining addends:

• rest of the sum negative: undefined sorted last, and the right === undefined early return in the "+" branch dropped it silently, giving a wrong entry
• rest of the sum positive: undefined sorted first, and left[0] threw the TypeError

Both symptoms are reachable from user input in DoenetML, where <math simplify>$A + $B - $C</math> over numeric matrices is common.

Fix

Return the accumulated number when there are no other factors, so the product collapses to 1 rather than to nothing.

Also in this PR

• Regression tests for both symptoms, plus the matrix negation and the tuple/vector forms of the same bug. All four fail on 2.x — two by assertion, one with the TypeError.
• Version bumped to 2.0.0-alpha96.
• build/ regenerated. It had not been rebuilt since Switch to Vite #68, so this also picks up the lib/mathjs.js change from Publish numeric on the global object so browsers can use it #86.

Full suite passes: 6194 tests across 29 files.

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