feat(fusion_accounting_bank_rec): reconcile engine 6-method public API

Adds fusion.reconcile.engine — the AbstractModel orchestrator for all
bank-line reconciliations. Six public methods (reconcile_one,
reconcile_batch, suggest_matches, accept_suggestion, write_off,
unreconcile) form the only sanctioned write path to
account.partial.reconcile from the rest of the module (controllers, AI
tools, wizards).

Implementation follows V19's bank_rec_widget pattern: rewrite the bank
move's suspense line into one counterpart per matched invoice (or a
write-off line) on the appropriate receivable / payable / write-off
account, then call account.move.line.reconcile() on each pair. Records
a precedent row per reconcile for downstream pattern learning.

16 new unit tests cover all six methods across happy paths, the
precedent side effect, suggestion lifecycle, batch auto-strategy, and
write-off line clearance. 67 total tests, 0 failed.

Made-with: Cursor

fusion_accounting_bank_rec/models/__init__.py

@@ -4,3 +4,4 @@ from . import fusion_reconcile_suggestion
 from . import fusion_bank_rec_widget
 from . import account_bank_statement_line
 from . import account_reconcile_model
+from . import fusion_reconcile_engine