Fix deepcopy RecursionError on World objects

[Copilot]

The run-notebook-demos-extra CI test fails with RecursionError: maximum recursion depth exceeded when demo_notebook_03en_pytorch calls copy.deepcopy(env.W) to save the best World state during RL training. The deeply nested object graph (World ↔ Node ↔ Link ↔ Vehicle chains) exceeds Python's default recursion limit of 1000 during recursive deepcopy traversal. The failure started from a dependency version bump (not a code change) that pushed the required depth past the limit.

• Add World.__deepcopy__ that temporarily raises sys.setrecursionlimit proportional to the number of simulation objects before delegating to standard deepcopy logic, restoring the original limit in finally

# Previously fails on large networks with default recursion limit
import copy
W2 = copy.deepcopy(W)  # RecursionError

# Now works — __deepcopy__ scales the limit to match the object graph
W2 = copy.deepcopy(W)  # OK, even with sys.setrecursionlimit(300)

• Fixes failure of run-notebook-demos-extra test #358