[13.x] Fix Number::pairs() infinite loop when $to or $by is non-finite

[Amirhf1]

Number::pairs() did not guard against non-finite $to/$by values, unlike its sibling methods
(fileSize(), forHumans(), trim()) in the same class, which already handle INF/NAN safely.

This currently produces three distinct bugs:

• Number::pairs(INF, 10) causes a fatal out-of-memory crash the loop condition $lower < $to never becomes false, so it iterates until PHP exhausts its memory limit.
• Number::pairs(NAN, 10) silently returns an empty array (any comparison against NAN is false, so the loop body never runs).
• Number::pairs(10, NAN) returns a bogus pair containing NAN.

This PR extends the existing validation in pairs() (which already throws for $by == 0) to also reject non-finite $to/$by, consistent with how the rest of the class handles this input.

Reproduction

​php Number::pairs(INF, 10); // Fatal error: Allowed memory size exhausted Number::pairs(NAN, 10); // [] (silently wrong) Number::pairs(10, NAN); // [[0, NAN]] (silently wrong) ​