fix(tholos): prevent resolver from voting when they are also asserter or disputer (#165)

[ZacLou]

Closes #165.

resolve previously allowed a resolver to vote on an assertion where they were also the asserter or disputer. In the degenerate case of a size-1 committee, a single address acting as both disputer and sole resolver could guarantee their own win with zero collusion.

Changes:

• Add Error::ResolverIsParty = 24.
• After the AlreadyVoted check, reject the call if resolver == assertion.asserter or assertion.disputer == Some(resolver).
• Add test_resolver_who_is_asserter_cannot_vote and test_resolver_who_is_disputer_cannot_vote, each constructing a committee that includes the party address and asserting ResolverIsParty.

[collinsezedike]

@ZacLou Closing. #165 has no assignee. You explicitly said you understood the workflow and would wait for assignment. You opened this anyway, and a second duplicate PR (#198) for the same issue on top of it.