Daml: check that the DSO party is validated before exercising in DsoRules

Follow up for https://github.com/canton-network/splice/pull/7839#issuecomment-6293471199

There are quite a few cases where the validation of a fetchChecked (ForDso with dso) cid is missing before we exercise on cid in DsoRules.

Let's do this quick validation and fix as part of M2 in the sense of the boyscout rule "Always leave the code you're editing a little better than you found it. "

Partial Set of Problematic Code

from a quick review, may not be complete:

• DsoRules_AdvanceOpenMiningRounds
• DsoRules_UpdateExternalPartyConfigStates
• DsoRules_ClaimExpiredRewardsV2
• DsoRules_UnhideRewardCouponsV2
• DsoRules_ArchiveDryRunRewardAccountingV2
• DsoRules_MergeUnclaimedRewards
• DsoRules_MergeUnclaimedDevelopmentFundCoupons
• DsoRules_MiningRound_Close
• DsoRules_MergeMemberTrafficContracts
• DsoRules_AmuletRules_ConvertFeaturedAppActivityMarkers