Refactor block range calculations for token and exchange events in Transfer/TransferApproval indexers

[purplesmoke05]

📌 Description

This pull request refactors and improves the logic for determining the starting block (fromBlock) when querying blockchain logs for both token and exchange events in the indexer_Transfer.py and indexer_TransferApproval.py files. The main goal is to ensure that log queries start from the correct minimum block for each target, preventing redundant or missed log retrievals, while also simplifying the code structure.

✅ Related Issues

• Related to Batch fetch logs and refactor event indexing (Transfer/TransferApproval) #1767

🔄 Changes

1. Improved Minimum Block Calculation Logic

• Introduced new static methods (__calculate_minimum_from_block_for_targets, __calculate_minimum_from_block_for_token_targets, and __calculate_minimum_from_block_for_exchange_targets) to accurately determine the minimum fromBlock for log queries based on per-target cursors or skip blocks, replacing the previous approach of using a single oldest_block_from value.

2. Refactored Mapping of Targets and Decoders

• Combined the mapping of targets and their event decoders into a single dictionary (target_by_address) that stores tuples of (target, event_decoder), eliminating the need for separate decoder dictionaries and reducing redundant lookups.

📌 Checklist

• I have added tests where necessary.
• I have updated the documentation where necessary.

[github-actions]

Coverage Report •

File	Stmts	Miss	Cover	Missing
batch/sub_indexers
indexer_Transfer.py	302	32	89%	95, 189–191, 247–251, 273, 294, 368–369, 392, 396, 423, 425, 465–466, 495, 512–513, 538–539, 568, 585–586, 611–612, 643, 660–661
indexer_TransferApproval.py	381	49	87%	99–102, 110–113, 155–159, 196, 220, 305–308, 376, 427–428, 467–468, 492–493, 506, 520–521, 543–544, 564–565, 589–590, 610–611, 635–636, 657–658, 770, 776–777, 779, 793, 799–800, 802
tests/batch/sub_indexers
indexer_Transfer_test.py	607	0	100%
TOTAL	37858	1732	95%

Tests	Skipped	Failures	Errors	Time
1268	0 💤	0 ❌	0 🔥	10m 2s ⏱️