nimiq-primitives: Out-of-bounds panic in KeyNibbles::Add from oversized child suffix in a deserialized proof

Impact A malicious peer acting as a state-sync source can crash a syncing node with a crafted TrieChunk whose proof contains a TrieNodeChild whose suffix, when concatenated with the parent key via KeyNibbles::Add, exceeds the fixed 63-byte backing array. Add primitives/src/keynibbles.rs:332 / :34...