test: migrate stats/incr/nanrmse to ULP-based assertions

[Planeshifter]

Description

What is the purpose of this pull request?

This pull request:

• migrates the tests of @stdlib/stats/incr/nanrmse from EPS/tolerance-based assertions to ULP-based assertions using @stdlib/assert/is-almost-same-value.
• passes the ULP count as an inline integer literal. All three call sites (the main fixture loop, the NaN-ignoring loop, and the no-argument "current value" test) were tightened from an initial 64 down to the measured minimum of 0 ULPs (results are exactly equal to the reference computation; the previous tolerance was 1.0 * EPS * abs(expected)). The suite was run twice at the final values with identical, passing results.
• removes the now-unused abs and EPS requires and the delta/tol variables.

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

• [RFC]: Migrate math/base/special packages from relative tolerance testing to ULP difference testing (tracking issue) #11352

Questions

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No.

Other

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No.

Checklist

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• Read, understood, and followed the contributing guidelines.

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This PR was written primarily by Claude Code as an automated routine.

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Coverage Report

Package	Statements	Branches	Functions	Lines
stats/incr/nanrmse	$\\color{green}129/129$ $\\color{green}+100.00\\%$	$\\color{green}8/8$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}129/129$ $\\color{green}+100.00\\%$

The above coverage report was generated for the changes in this PR.