Fix is-int and is-float; add tests

[c71n93]

Closes #146

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PR-Codex overview

Focus of this PR:

This PR focuses on adding new methods to the number class in the math package. These methods check if a number is equal to zero, whether it is an integer or a float, and if it is NaN.

Detailed summary:

• Added a new method is-int-zero to check if a number is an integer zero.
• Added a new method is-float-zero to check if a number is a floating-point zero.
• Added a new method is-nan to check if a number is NaN.
• Added test cases to verify the functionality of the new methods.

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[c71n93]

@maxonfjvipon could you check this one, please?

[maxonfjvipon]

@c71n93 Good one! Just a several comments from my side

[maxonfjvipon]

@c71n93 let's make a minor optimization and replace 0.0.as-bytes with 00-00-00.... The same story with -0.0.as-bytes below

[maxonfjvipon]

@c71n93 or at least you can cache 0.0.as-bytes

[c71n93]

@maxonfjvipon done

[c71n93]

@yegor256 could you check this one, please?

[yegor256]

@rultor merge

[rultor]

@rultor merge

@yegor256 OK, I'll try to merge now. You can check the progress of the merge here

[rultor]

@rultor merge

@yegor256 Done! FYI, the full log is here (took me 6min)