bug: normalizeIPv6 does not normalize correct when double colon is already added

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### Issue

normalizeIPv6 in utils can not properly normalize IPv6 addresses. Hard to describe, so here an example:

`::0000:1` has to be normalized to `::1` but it is normalized to `:::1`
`1::1:0:0:1`has to be normalized to `1::1:0:0:1`but is normalized to `1::1:::1`

So basically in the normalizeIPv6 function we have to track if we already added the double colon, and if so, dont add again a double colon.
Also if we have added a double colon following hextets with 0 need to be written out.

In #88 I modified already the stringArrayToHexStripped I added a second parameter called keepZero. So if we already added a double colon followed by a non-zero hextet, we have to track to keep the zero and if we have following 0 hextets we have to set in stringArrayToHexStripped the parameter keepZero to true.