Malfeasance V2: Double Post

[fasmat]

Description

Contextual validation includes a check that verifies that the same identity didn't participate with their PoST in two different ATXs. In ATX v1 this was known as a Double Publish Proof and proofed that two ATXs were created by the same identity for the same publish epoch.

In ATX v2 this needs to be changed to proof that the same identity provided their PoST to two different ATXs, since the identity in question might not have signed the ATX.

Implementation hints

The malfeasance proof needs to include the following data to be valid:

1. The provided post(s) must be valid - otherwise the "Invalid Post" malfeasance proof should be used, see Malfeasance V2: Invalid Post #6141
2. The provided post must have been included by an identity that is part of the same marriage set as the identity that created the post. This requires the malfeasance proof to include proof about the marriage of the identities involved.
3. The ATXs including the PoSTs by the same identity must have been published in the same epoch.

[fasmat]

Closed because it can be replaced with #6309