feat: add withdrawal tx info

[jeremy-babylonlabs]

No description provided.

[Copilot]

Pull Request Overview

This PR adds withdrawal transaction information to the delegation data structures, enabling the API to expose withdrawal transaction details when available.

Key Changes:

• Added WithdrawalTx struct to the database model layer with transaction details and timestamp
• Added corresponding WithdrawalInfo struct to the service layer with ISO-formatted timestamp
• Implemented conditional mapping logic to include withdrawal info in API responses when present

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
internal/indexer/db/model/delegation.go	Defines WithdrawalTx struct with BSON tags and adds it as an optional field to IndexerDelegationDetails
internal/v2/service/delegation.go	Defines WithdrawalInfo struct with JSON tags, adds it to DelegationPublic, and implements mapping logic in FromDelegationDocument

The implementation is clean and follows established patterns in the codebase. The changes properly handle optional withdrawal data by checking for non-empty transaction hash before mapping, consistent with how unbonding transactions are handled elsewhere. The use of appropriate struct tags (bson for database, json for API) and omitempty flags ensures proper serialization at each layer.

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[kirugan]

what about existing delegations? should we run a migration?

[jrwbabylonlab]

i think it's fine.... until someone ask for it.

[jrwbabylonlab]

optional