Replace v == zero(v) with _iszero

[OlivierHnt]

The purpose of this PR is to not call == directly, and use _iszero instead. This is to help integration with IntervalArithmetic.jl since == for our Interval type does not always return a Boolean.

Closes #609.

I did not change two checks using === since this would break the behaviour for -0.0. If I understood correctly, it should not be an issue with Interval, since it will return false consistently (it may be sub-optimal, but not wrong)
cc @dpsanders, @Kolaru
cc also @kalmarek, since you raised JuliaIntervals/IntervalArithmetic.jl#628 you may have more experience mixing SparseArrays and IntervalArithmetic

I do not know how to the backporting procedure works, but it'd be great to have this for 1.10 and 1.11.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.08%. Comparing base (f3610c0) to head (974a391).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #610   +/-   ##
=======================================
  Coverage   84.08%   84.08%           
=======================================
  Files          12       12           
  Lines        9192     9192           
=======================================
  Hits         7729     7729           
  Misses       1463     1463           

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[ViralBShah]

@SobhanMP