fixes #23513, parseutils.nim: parseInt's doc example.

[litlighilit]

fixes #23513

Also, the old runnableExample is just a copy of proc parseInt(openArray[char], var int, int) variant (in Line 1000).

[litlighilit]

I find...

• Any procedure that's related to parse some integers handles underline _ (e.g. parseOct/parseHex ¹ )
• parseInt parseBiggestInt handles leading sign character +/-.

Mentioned in here

I think we shall either:

• Mention what they can handle in their doc comments
• Or just reflect these in runnableExamples as they used to do.

Footnotes

1. This is reflected in their runnableExamples ↩

[litlighilit]

• Or just reflect these in runnableExamples as they used to do.

Currently I've added examples for all parseInt/parseBiggestInt variants in std/parseutils

[litlighilit]

ping @ringabout

[litlighilit]

@ringabout
any improvement needed?

---

If such a feature is really required to be metioned in doc comment, not only runnableExamples, then I'll update all doc of these procs metioned here.

[github-actions]

Thanks for your hard work on this PR!
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