Fix Issue 22170: Add abs(), rem(), urem() and improve docs

[Adityazzzzz]

Fixes Issue #22170.

Changes:

• Added abs() helper function to core.int128.
• Added rem() (signed) and urem() (unsigned) wrapper functions.
• Updated documentation for mul, div, and sar to clarify signed/unsigned behavior.
• Added unit tests.

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Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#22226"

[rikkimax]

It would be good for a follow-up PR to add the overflow of signed/unsigned multiply that Iain mentioned in the ticket, if you are able to do so.

[Adityazzzzz]

I have updated the changes in the PR, Please review

[Adityazzzzz]

It would be good for a follow-up PR to add the overflow of signed/unsigned multiply that Iain mentioned in the ticket, if you are able to do so.

Sure! I will take a look at that in a separate PR once this is merged

[rikkimax]

More space removal.

[rikkimax]

More

[rikkimax]

Indent.

[rikkimax]

Again.

[Adityazzzzz]

Done! I've implemented the changes.
Please review

[ibuclaw]

Perhaps add check that unsigned mod/remainder matches the % operator?

Suggested change

	assert(rem(Cm10, C3) == Cm1); // -10 % 3 = -1
	assert(rem(Cm10, C3) == Cm1); // -10 % 3 = -1
	assert(urem(Cm10, C3) == C0); // -10U % 3 = 0