Fix spl token indexer parsing

[dharit-tan]

Description

Fix the parsing function in spl token indexer to lookup account indices correctly (same way as we do in index_user_bank.py). This was the bug that was causing us to skip certain transactions if accountKeys were not in a specific order.

Tests

Updated spl token indexer unit test to include 2 purchase transactions with different accountKeys ordering.

Monitoring - How will this change be monitored? Are there sufficient logs / alerts?