L-05 Missing Check for Duplicate Addresses in _validatePChainOwner

[geoff-vball]

Why this should be merged

The _validatePChainOwner function ensures that PChainOwner meets the validation criteria outlined in the ACP-77 specification. It correctly checks that if the threshold is 0, the address list is empty, and that the threshold does not exceed the number of addresses. It also verifies that addresses are sorted in ascending order. However, it does not explicitly check for duplicate addresses, which is required by the ACP-77 specification.

If duplicate addresses are allowed, it could lead to unintended behavior when validating ownership thresholds, potentially enabling improper authorization or quorum calculations. This could pose security risks, as the system might incorrectly count duplicate addresses towards the threshold, leading to unintended validator permissions or incorrect staking assignments.

How this works

How this was tested

Unit test

How is this documented

[iansuvak]

Now we have a single error type for two types of user errors but I think that this is fine.