Fix TypeError in vacuum_lakehouse_tables() when retain_n_hours is None

[Copilot]

Since 0.16.0, vacuum_lakehouse_tables() builds the retention_period string via retain_n_hours // 24, which raises TypeError: unsupported operand type(s) for //: 'NoneType' and 'int' when retain_n_hours is left at its documented default of None. The documented behavior ("the default retention period configured for the Delta table will be used") was only true prior to 0.16.0, when the function passed retain_n_hours straight through to _vacuum_table().

Changes

• src/sempy_labs/lakehouse/_lakehouse.py — compute retention_period once, before the loop, and only when retain_n_hours is provided:

  if retain_n_hours is None:
      retention_period = None
  else:
      days, hours = divmod(retain_n_hours, 24)
      retention_period = f"{days}:{hours:02d}:00:00"

  run_table_maintenance() already omits retentionPeriod from the API payload when it is None, so no change is needed there — the table's own configured retention applies. Zero-padding behavior from Fix vacuum_lakehouse_tables retention period formatting for single-digit hours #1309 is preserved.

• tests/test_lakehouse.py — extracted the monkeypatch setup into a _patch_lakehouse helper and added a regression test asserting retention_period is None when the function is called without retain_n_hours.

• Fixes vacuum_lakehouse_tables() fails with TypeError when using documented default retain_n_hours=None (regression in 0.16.0) #1322