Generic kadkey

[iand]

When https://github.com/golang/go/issues/44253 is implemented we could replace any by [...]byte

[guillaumemichel]

In order to remove the errors returned from KadKey methods, we can simply accept any size of key, and move the responsibility to check the key size to the caller.

When an method is called on 2 keys of different size, consider that the shorter one is a prefix (aligned left). Just like if we pad right zeros to the shortest key.

• Equal would return true iff the keysize is the same for both keys, and all bits are the same
• Compare with 2 different key sizes would compare the bits of the 2 keys up to the size of the shortest key. If key0[:shortestKeyLen]==key1[:shortestKeyLen], consider that shortest_key < longest_key. Return 0 iff key0.Equal(key1).
• CommonPrefixLength returns the actual CPL (given that the shortest key is a prefix, and not a suffix), so CPL <= shortestKeyLen
• Xor normally xors longestKey and shortestKey+"00"*(longestKeyLen-shortestKeyLen). So the last bits of longestKey stay unchanged