fix(kademlia): neighborhood rebroadcast sends wrong peer lists

[gacevicljubisa]

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• I have read the coding guide.
• My change requires a documentation update, and I have done it.
• I have added tests to cover my changes.
• I have filled out the description and linked the related issues.

Description

The 15-minute neighborhood rebroadcast in the Kademlia manage loop previously built each peer's broadcast list using append(neighbors[:i], neighbors[i+1:]...). Because neighbors[:i] shares the backing array of the slice being iterated over, the slice was overwritten in-place starting from the second iteration.

For example, with four neighbors [a b c d], the loop produced:

i=0 -> a: [b c d]   (neighbors mutated to [b c d d])
i=1 -> c: [b d d]
i=2 -> d: [b d d]
i=3 -> d: [b d d]

As a result, only the first peer received the correct list, b was skipped, d was notified twice and told about itself, and the lists contained duplicates.

Open API Spec Version Changes (if applicable)

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• This PR contains code that has been generated by an LLM.
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[martinconic]

The PR description is out of sync with the latest commit (c97300d). It still mentions exporting RebroadcastNeighborhood in export_test.go and adding TestRebroadcastNeighborhood with storage radius 0, both of which were removed in the second commit.