Improve TDT for `campaign`

[lumtis]

Part of https://github.com/tendermint/spn/issues/556

Considered for improvement:

• keeper/grpc_campaign_summary_test.go
• keeper/grpc_special_allocations_balance_test.go
• keeper/msg_burn_vouchers_test.go
• keeper/msg_create_campaign_test.go
• keeper/msg_edit_campaign_test.go
• keeper/msg_initialize_mainnet_test.go
• keeper/msg_mint_vouchers_test.go
• keeper/msg_redeem_vouchers_test.go
• keeper/msg_unredeem_vouchers_test.go
• keeper/msg_update_special_allocations_test.go
• keeper/msg_update_total_supply_test.go
• types/campaign_test.go
• types/genesis_test.go