fix: harden ledger skip invariant

Co-authored-by: genichin <4282227+genichin@users.noreply.github.com>

trex_core/adapters/persistence/ledger_skip_store.py

@@ -98,7 +98,8 @@ class PostgreSQLLedgerSkipStore:
                 )
             conn.commit()
         record = self.get(skip_key)
-        assert record is not None
+        if record is None:
+            raise RuntimeError(f"ledger_skip row missing after upsert for key {skip_key!r}")
         return record, notify
 
     def get(self, skip_key: str) -> LedgerSkipRecord | None: