Implement deletion of missing jettons and nfts

[danoctua]

Implement deletion of missing jettons and nfts

Description

Implemented logic to correctly prune Jetton Wallets and NFT Items that are no longer returned by the indexer-blockchain API. Previously, items that were transferred out or had zero balance (and thus disappeared from the API response) remained in the database as stale data. Use a chunked deletion strategy to handle large datasets efficiently.

Checklist

Before submitting your pull request, please ensure the following:

• I have read the contributing guidelines.
• I ran all tests and they passed successfully.
• I added/updated documentation (if applicable).
• I reviewed my own code and followed the project's code style.
• I included relevant details in the PR description or commit messages.

Changes

• Refactor: Added delete_missing methods to JettonWalletService and NftItemService which identify and delete stale records.
• Feat: Updated indexer_blockchain/tasks.py to invoke these deletion methods after fetching current wallet details.
• Perf: Implemented chunked deletion using core.utils.misc.batched to avoid SQL parameter limits.
• Test: Added comprehensive unit tests in tests/unit/core/services/test_sync_logic.py.
• Test: Added factories UserWalletFactory, JettonWalletFactory, NftItemFactory to support testing.

How Has This Been Tested?

Ran new unit tests using pytest tests/unit/core/services/test_sync_logic.py. Verified that:

• Jetton Wallets missing from the keep list are deleted.
• NFT Items missing from the keep list are deleted.
• Existing items in the keep list are preserved.
• Empty keep list results in full deletion of user's items.

Additional Notes

Factories were created (backend/tests/factories/wallet.py, backend/tests/factories/nft.py) to facilitate these tests and future testing needs.