…sensor

The kspaceFirstOrder3D simulation function was unintentionally modifying
the input `source` and `sensor` objects. This occurred because the
internal `kWaveSimulation` object and its helper functions were
operating directly on these mutable input objects.

This commit addresses the issue by:
1. Modifying `kWaveSimulation.__init__` to create deep copies of the
   input `source` and `sensor` objects. All internal operations within
   `kWaveSimulation` and its helper functions (like `save_to_disk_func`
   and `retract_transducer_grid_size`) now use these copies.
   The original objects you passed remain unchanged.

2. Adding a regression test (`tests/test_kspaceFirstOrder3D_state.py`).
   This test verifies that critical attributes of the `source` and
   `sensor` objects (e.g., `source.p0`, `sensor.mask`) are not altered
   after calls to `kspaceFirstOrder3D`, and that the function can be
   called multiple times with the same input objects without error or
   state corruption.

This ensures that the `source` and `sensor` states remain consistent,
allowing them to be reused for multiple simulations or checkpointing
without unexpected side effects, resolving bug #600.