feat(fusion_accounting_reports): drill_down_resolver service

Pure-Python helper that, given an account_id and a date range, fetches
posted account.move.line records and returns a flat list of dicts ready
for the drill-down OWL dialog. Used by the engine's drill_down() method.

3 new tests, 35 total passing.

Made-with: Cursor

fusion_accounting_reports/__manifest__.py

@@ -1,6 +1,6 @@
 {
     'name': 'Fusion Accounting Reports',
-    'version': '19.0.1.0.2',
+    'version': '19.0.1.0.3',
     'category': 'Accounting/Accounting',
     'summary': 'AI-augmented financial reports (P&L, balance sheet, trial balance, GL).',
     'description': """