Add initial self-delegation check in token handler

[Sigri44]

Fix self-delegate calculation for our community

[boundless-forest]

Please take a review and ensure it not breaks our existing voting power calculation logic. @fewensa

[fewensa]

What this fixes

This PR fixes a vote-power double-materialization bug in the indexer triggered by a specific event combination: an initial self-delegation and an incoming transfer occurring in the same transaction.

The exact scenario:

1. An address has never delegated before
2. It performs its first self-delegation in a transaction (DelegateChanged: 0x0 → self)
3. The same transaction also delivers an incoming token transfer to that address
4. By the time the transfer handler runs, the rolling record for the delegate change is already visible

Under this condition, the old logic on main allows both the transfer path and the DeligateVotesChanged path to materialize the self-edge independently, causing relation power and contributor power to be overstated.

How it is fixed

The change is in isTransferToCoveredByDelegateChange(). Previously this function always returned false for the transfer-to direction, meaning an incoming transfer was never considered covered by a same-transaction delegate change.

This PR makes it return true when all three conditions hold:

• fromDelegate == 0x0 (delegating from the undelegated state)
• toDelegate == delegator (delegating to self)
• delegator == transfer.to (the delegator is the recipient of this transfer)

With this in place, storeTokenTransfer() correctly recognizes that the incoming transfer is already covered by the same-transaction initial self-delegation and skips the redundant materialization.

Relationship to #639

This is a narrow follow-up hardening patch after #639. Both target the same general bug family (same-transaction DelegateChanged + Transfer + DelegateVotesChanged interactions) but cover different subcases — they complement rather than replace each other.

Recommendation

The logic change is directionally correct. However the PR is missing a targeted regression test. A focused test case should be added to token-vote-power.test.ts covering the full event sequence of "delegate change before transfer, initial self-delegation", asserting that the final DelegateMapping, Delegate, Contributor, and DataMetric contain no duplicate power accumulation before this is merged.

---

Regression testing needs to be added.