test(fusion_accounting_reports): coexistence behavior

Mirrors Phase 1's coexistence test pattern. Verifies:

- The coexistence group (group_fusion_show_when_enterprise_absent)
  exists and is referenceable
- The reports engine model (fusion.report.engine) is always
  registered, regardless of Enterprise install state
- The Financial Reports root menu requires the coexistence group
- The Open Report... sub-menu (period picker wizard) is gated too

Uses V19 group_ids attribute with a graceful fallback to groups_id for
older runtime variants.

Tests: 3 new (test_coexistence.py). Net 115 -> 118.
Made-with: Cursor

fusion_accounting_reports/__manifest__.py

@@ -1,6 +1,6 @@
 {
     'name': 'Fusion Accounting Reports',
-    'version': '19.0.1.0.34',
+    'version': '19.0.1.0.35',
     'category': 'Accounting/Accounting',
     'summary': 'AI-augmented financial reports (P&L, balance sheet, trial balance, GL).',
     'description': """