MNT: lint sweep for the solution refactor

Move the Solution import in _encoders to module scope (no import cycle) and
document the unused NumPy-protocol argument on Solution.__array__.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: MateusStano

rocketpy/_encoders.py

@@ -9,6 +9,7 @@
 from rocketpy.mathutils.function import Function
 from rocketpy.plots.flight_plots import _FlightPlots
 from rocketpy.prints.flight_prints import _FlightPrints
+from rocketpy.simulation.solution import Solution
 
 
 class RocketPyEncoder(json.JSONEncoder):
@@ -199,8 +200,6 @@ def set_minimal_flight_attributes(flight, obj):
 
     # The solution is stored either as the new segment-based dict or, for older
     # saved flights, as a flat list of canonical rows.
-    from rocketpy.simulation.solution import Solution
-
     raw_solution = obj["solution"]
     if isinstance(raw_solution, dict):
         flight.solution = Solution.from_dict(raw_solution)

rocketpy/simulation/solution.py

@@ -594,7 +594,9 @@ def pop(self, index=-1):
         self._version += 1
         return row
 
-    def __array__(self, dtype=None, copy=None):
+    def __array__(self, dtype=None, copy=None):  # pylint: disable=unused-argument
+        # `copy` is part of the NumPy array protocol; the array is always freshly
+        # built here, so it is accepted for compatibility and not acted on.
         widths = {segment.width for segment in self._segments if segment.rows}
         if len(widths) > 1:
             raise TypeError(