A power of a constant below 1e-50 is no longer simplified to zero

[Rafael-SOWNet]

Closes #1769.

1/pi^136, about 2.4e-68, inner-simplified to 0, and so did any product, quotient or power of constants below 1e-50. Simplify raises constants to such powers on its way, and returned 0 for expressions that are not zero:

expression	2.5.0	master 85d6601c	this
1/pi^136, inner-simplified	0	0	1/pi^136
e^(-160), inner-simplified	0	0	e^(-160)
pi^(-136) + pi^(-137), inner-simplified	0	0	as written
x^n ((1 - d^2)/x - x)^3 (1 + x^2 - d x)/(x - d)/pi^2, simplified	0 provided ...	0 provided ...	itself, rearranged

What changes. Evaluation rounds a value within 1e-50 of an integer onto the integer, half the default hundred digits, which is what makes the residual of a cancellation -- sin(pi)'s, sqrt(2)^2 - 2's -- the zero it is; and inner simplification takes a node's value wherever that value is an exact number. A product cancels nothing, so a zero there is rounding alone: 1/pi^136 evaluated to 0, and that 0 was taken as its value. The shortcut passes over such a zero now where the node is a product, a quotient or a power of numbers and constants none of which is zero, or a sum of such of one sign, and the node is kept as written. Evaluation is unchanged: "1/pi^136".EvalNumerical() is 0 as before, the rounding being the setting's.

Where it showed. The integrator simplifies an integrand under a substitution, and answered e x^n (((a e f^2 - d^2 e)/(e x) - x)/2 + x)^3 (4 x (x - d) - 2 ((x - d)^2 - a f^2))/(f^3 (2 e x)^2), with Euler's e, as 0. The derivation of the last row's Simplify reaches (pi^136)^(-1), and its value is lost at that node's inner simplification.

Tests: PowerOfAConstantBelowTheToleranceTest: six expressions not rounded to zero, compared exactly with a rational for each constant; two cancellations still zero; and Simplify keeping the last row's value at a point. On master eight of its ten fail.

The full suite on the head, f1f8bfee, passes, 14,934 tests, and the allocation gate passed on the change; the library builds for netstandard2.0. The head is one commit on master 85d6601c.

🤖 Generated with Claude Code

https://claude.ai/code/session_012sonx8iAspMiwRwokT1Ura