Refund ecosystem account when invalid topic to reward

[guilherme-brandao]

Purpose of Changes and their Description

This PR modifies the rewards distribution logic to handle cases where a topic is eligible for rewards based on its weight but cannot distribute them due to lack of active participation (e.g., no reward nonce submitted or errors during reward processing).

Previously, these rewards might have remained undistributed in the rewards module. Now, any rewards allocated to a topic that cannot be processed are transferred to the EcosystemModuleName account.

Changes:

• Added keeper.MoveCoinsFromAlloraRewardsToEcosystem function to facilitate the transfer.
• Updated rewards.EmitRewards to call the new keeper function when a topic's rewards cannot be processed.
• Added the test case TestNoActiveParticipantsNoRewardsForTopic to verify that rewards for topics without active participation are correctly moved to the ecosystem module account.

Link(s) to Ticket(s) or Issue(s) resolved by this PR

https://linear.app/alloralabs/issue/ENGN-3525/189-185-apy-over-12percent

Are these changes tested and documented?

• If tested, please describe how. If not, why tests are not needed.
• If documented, please describe where. If not, describe why docs are not needed.
• Added to Unreleased section of CHANGELOG.md?

[xmariachi]

ok, lgtm!
Approving preemptively.
My only suggestion would be to accumulate the rewards to be given back, to optimize the sending of rewards for all failing topics in one go, instead of having one per failing topic. In practice, since it's such an uncommon scenario, it shouldn't matter that much.