fix(auto-fixer): strip spurious .reset_index() after .transform() calls

LLM sometimes copies the .reset_index(level=N, drop=True) suffix from
groupby().rolling().method() patterns and adds it after .transform(),
but transform() already preserves the original index. The extra
reset_index() drops an index level and causes ValueError: 'cannot reindex
on an axis with duplicate labels' or shape mismatch on assignment.

Detect: any line containing both .transform( and .reset_index(level=..., drop=True)
Fix: strip the .reset_index() suffix from those lines.

Adds 1 new test (test_transform_reset_index_stripped) — total 30 tests.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test/qlib/test_auto_fixer.py

@@ -197,6 +197,13 @@ class TestGroupbyApplyToTransform:
         assert "lambda x: x.cumsum()" in result
         assert ".transform(" in result
 
+    def test_transform_reset_index_stripped(self, fixer):
+        # .transform() already preserves index — .reset_index() after it is wrong
+        code = "df['v'] = df.groupby(level=1)['x'].transform(lambda x: x.rolling(20).mean()).reset_index(level=0, drop=True)"
+        result = fixer.fix(code)
+        assert ".reset_index(level=0, drop=True)" not in result
+        assert ".transform(" in result
+
 
 class TestRollingDdof:
     def test_removes_ddof_from_rolling_args(self, fixer):