feat: optimize blockchain indexer with single-query NFT and last_activity skip

[danoctua]

feat: optimize blockchain indexer (single-query NFT & last_activity skip)

Description

This pull request optimizes the indexer-blockchain service to reduce TonAPI traffic (currently >1TB/day) and database load.

1. Elimination of N+1 NFT Queries: Instead of looping through all 80+ whitelisted NFT collections and making an API request for each, we now query all user-owned NFTs in a single, unfiltered API request.
2. last_activity-Based Skipping: We store the blockchain's last_activity timestamp on the user's wallet. If the timestamp hasn't changed since the last check, we skip the entire Jettons/NFTs fetch, saving
   significant network traffic and DB operations.
3. Database Migration Bugfix: Fixed an issue where the existing migration 1750345690-ec82e8aa0d67-telegram_chat_rule_group.py crashed on empty/clean databases due to parameter binding on an empty list.

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. - [x] I included relevant details in the PR description or commit messages.

Changes

• Single-Query NFT Fetch: Updated get_all_nfts_per_user in tasks.py to fetch all user NFTs at once.
• In-Memory NFT Pre-filtering: Added in-memory filtering against whitelisted collection addresses in tasks.py before passing NFT items to bulk_create_or_update and delete_missing, preventing unnecessary queries for non-whitelisted items.
• Wallet Model Update: Added last_activity (BIGINT) to UserWallet and generated a database migration.
• Sync Skipping: Refactored fetch_wallet_details to check last_activity returned from get_account_info at the start of the task against the database, skipping Jetton and NFT fetches entirely if they are equal.
• Atomic updates: Modified WalletService.set_balance to update last_activity atomically within the database update transaction.

How Has This Been Tested?

• Added unit tests in backend/tests/unit/indexer_blockchain/test_tasks.py covering:
  • Initial sync behavior when last_activity is None.
  • Skip behavior when last_activity is unchanged.
  • Sync trigger behavior when last_activity is updated on the blockchain.
• Ran the full test suite on a clean, dockerized test database. All 99 unit tests passed successfully.