fix: node allocator

[sergelogvinov]

Pull Request

What? (description)

If a node has a large subnet, such as a /56 or larger, we need to allocate a /64 subnet for each individual node.

Why? (reasoning)

Acceptance

Please use the following checklist:

• [ ] you linked an issue (if applicable)
• [ ] you included tests (if applicable)
• [ ] you ran conformance (make conformance)
• [ ] you linted your code (make lint)
• [ ] you linted your code (make unit)

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[sergelogvinov]

/m