[Swaps] Support setting a Rikiddo pool for scalar markets to stale

[sea212]

Currently distribute_pool_share_rewards assumes that only one outcome asset will remain as the resolved outcome. It should be aware of scalar pools and in case of scalar pool should:

• burn both LONG and SHORT in pool account
• take total issuance of LONG and SHORT
• amm_profit = total_issuance - (outcome_short * SHORT + outcome_long * LONG)
• continue as before after amm_profit was calculated

In addition to that, set_pool_as_stale should call Rikiddo and distribute_pool_share_rewards properly for pools with scalar outcome assets.