base loader: fix micro batch is_processed marking, add tests

[fordN]

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[github-actions]

🎨 Ruff Formatting & Linting Report

Run the following commands locally to fix issues:

ruff format .
ruff check . --fix

Formatting changes needed:

--- src/amp/loaders/base.py
+++ src/amp/loaders/base.py
@@ -634,7 +634,9 @@
         try:
             # Delegate to loader-specific transactional implementation
             # Loaders that support transactions implement load_batch_transactional()
-            rows_loaded_batch = self.load_batch_transactional(batch_data, table_name, connection_name, ranges, ranges_complete)
+            rows_loaded_batch = self.load_batch_transactional(
+                batch_data, table_name, connection_name, ranges, ranges_complete
+            )
             duration = time.time() - start_time
 
             # Mark batches as processed ONLY when microbatch is complete

--- tests/integration/test_postgresql_loader.py
+++ tests/integration/test_postgresql_loader.py
@@ -803,9 +803,7 @@
             assert len(duplicate_results) == 1
             assert duplicate_results[0].success is True
             assert duplicate_results[0].rows_loaded == 0, 'Duplicate microbatch should be skipped'
-            assert (
-                duplicate_results[0].metadata.get('operation') == 'skip_duplicate'
-            ), 'Should be marked as duplicate'
+            assert duplicate_results[0].metadata.get('operation') == 'skip_duplicate', 'Should be marked as duplicate'
 
             # Verify row count unchanged (duplicate was skipped)
             conn = loader.pool.getconn()

--- tests/integration/test_snowflake_loader.py
+++ tests/integration/test_snowflake_loader.py
@@ -1207,9 +1207,7 @@
             assert len(duplicate_results) == 1
             assert duplicate_results[0].success is True
             assert duplicate_results[0].rows_loaded == 0, 'Duplicate microbatch should be skipped'
-            assert (
-                duplicate_results[0].metadata.get('operation') == 'skip_duplicate'
-            ), 'Should be marked as duplicate'
+            assert duplicate_results[0].metadata.get('operation') == 'skip_duplicate', 'Should be marked as duplicate'
 
             # Verify row count unchanged (duplicate was skipped)
             loader.cursor.execute(f'SELECT COUNT(*) as count FROM {test_table_name}')

3 files would be reformatted, 94 files already formatted

Linting issues:

E501 Line too long (127 > 120)
   --> src/amp/loaders/base.py:637:121
    |
635 |             # Delegate to loader-specific transactional implementation
636 |             # Loaders that support transactions implement load_batch_transactional()
637 |             rows_loaded_batch = self.load_batch_transactional(batch_data, table_name, connection_name, ranges, ranges_complete)
    |                                                                                                                         ^^^^^^^
638 |             duration = time.time() - start_time
    |

Found 1 error.