feat(billing): 2a NexaCloud→Odoo importer (read-only, idempotent, shadow-safe)

fusion.billing.import.wizard backfills NexaCloud into Odoo: read-only
psycopg2 reader (_read_nexacloud_rows, DSN from ir.config_parameter)
split from pure-Odoo writes (_import_rows/_do_import) so the logic is
unit-tested headless. Maps users→partners+links (reusing
_resolve_or_create_partner, stashing stripe_customer_id), plans→a
cpu_seconds charge catalog (included_quota=cpu_seconds_quota,
unit_batch=3600, $0.0075/core-hour, plan_id NULL), and deployments→one
DRAFT shadow sale.order per deployment with the flat price set
explicitly. Shadow-safe by construction: draft + no payment token +
charge plan_id NULL (rating cron is a no-op). Idempotent re-runs;
per-row savepoints isolate bad rows; dry-run rolls back. 11 tests,
50/50 green on odoo-trial.

fusion_centralize_billing/models/sale_order.py

@@ -7,6 +7,16 @@ from odoo import api, fields, models
 class SaleOrder(models.Model):
     _inherit = "sale.order"
 
+    x_fc_nexacloud_subscription_id = fields.Char(
+        index=True, copy=False,
+        help="Source NexaCloud subscription id — the importer's idempotency key.")
+    x_fc_nexacloud_deployment_id = fields.Char(index=True, copy=False)
+    x_fc_billing_service_id = fields.Many2one(
+        "fusion.billing.service", index=True, copy=False, ondelete="set null")
+    x_fc_shadow = fields.Boolean(
+        default=False, copy=False,
+        help="Imported in shadow mode: Odoo computes but must not charge/post/email.")
+
     def _fc_rate_usage(self, charge, period_start, period_end):
         """Aggregate this subscription's usage for `charge`'s metric in the period,
         compute the overage amount, and upsert a matching overage order line.