Handle potential race conditions when creating models in DB

[jtourkos]

Description:

Right now we call:

const accountSeenEvent = await AccountSeenEventModel.create(
  {
    accountId,
    repoAccountId,
    receiverAccountId,
    refundAccountId,
    deadline,
    logIndex,
    blockNumber,
    blockTimestamp,
    transactionHash,
  },
  { transaction },
);

This is fine because we only run one instance of the service today.
However, if we scale horizontally (multiple workers/processes), two inserts of the same (transactionHash, logIndex) could happen concurrently. Since that pair is our composite primary key, the second insert would throw a SequelizeUniqueConstraintError.

Note:
This is just one example (AccountSeenEvent). We currently have similar Model.create(...) logic in multiple places across the codebase. The same race condition could appear anywhere we rely on PKs/unique keys to enforce idempotency.

Impact:

• No data corruption (the PK/unique constraints prevent duplicates).
• But in multi-instance setups we’ll see noisy errors unless we handle them gracefully.

Proposed solution:
Introduce an idempotent wrapper (e.g. ensureModelCreated(...)), that:

• Tries create.
• If a PK/unique conflict occurs, fetches and returns the existing row.
• Otherwise rethrows.