Fix reciprocal power simplification loop

[belomaxorka]

Fixes #3693.

simplify never terminates on (1/(x*(y-1)))^(1/(y-1)), and on symbolic powers of any reciprocal product.

Cause

n/n1 -> n*n1^-1 rewrites 1/X as 1 * X^-1. Distributing a power over that product leaves a 1^n factor, and nothing in the rule set removes it. Each pass creates a fresh one and merges it into the accumulated factor through n^n1 * n^n2 -> n^(n1+n2), so the exponent keeps growing and the expression string never repeats:

(1 / (x * y)) ^ z
(1 ^ z) * (((1 / x) / y) ^ z)
((1 ^ z) ^ 2) * (((1 / x) / y) ^ z)
(1 ^ (3 * z)) * (((1 / x) / y) ^ z)
(1 ^ (4 * z)) * (((1 / x) / y) ^ z)
...

_simplify stops when it revisits a string, so it loops forever. simplifyCore already folds n^0 and n^1, but not 1^n.

Change

One rule, 1^n -> 1, placed after the power distribution rules so the unit factor is removed where it is created.

Effect on existing results

Checked 1766 expressions against the current develop:

• 1285 unchanged;
• 143 previously non-terminating, now converge — no expression that converged before loops now, and no new errors;
• 338 changed, and in every one of them the develop output contained a stray 1 ^ ... factor that is now gone, for example 1 ^ z * (x + 1) ^ z / 2 ^ z becomes (x + 1) ^ z / 2 ^ z.

All 338 changed outputs were compared numerically against the develop output at 20 points each with complex-aware comparison: no differences. The 143 newly converging results were compared against their original expressions the same way: no differences.

The output form of expressions that already worked is otherwise untouched — 1/x^2 stays 1 / x ^ 2 and x^(-2) stays x ^ (-2).

Tests

should terminate when simplifying symbolic powers of reciprocals covers five looping expressions with a pass counter that fails instead of hanging the runner, asserts the simplified form and checks it numerically against the original. should remove unit factors raised to a power covers the rule itself. Both fail on develop and pass here. One case was added to the non-commutative-multiplication block.

npm run test:all passes on Node 26: 6654 source, 36 generated and 295 node tests, plus tsc and the TypeScript tests. eslint --max-warnings 0 is clean.