DEP: remove __next__ from Expr

[Zeroto521]

call next to a dict won't work.

In [14]: from pyscipopt import Model

In [15]: x = m.addVar()

In [16]: next(x)
---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
Cell In[16], line 1
----> 1 next(x)

StopIteration:

In [17]: next(x+1)
---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
Cell In[17], line 1
----> 1 next(x+1)

StopIteration:

In [18]: next(abs(x))
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[18], line 1
----> 1 next(abs(x))

TypeError: 'pyscipopt.scip.UnaryExpr' object is not an iterator
In [19]: next({1:1, 2:2})
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[19], line 1
----> 1 next({1:1, 2:2})

TypeError: 'dict' object is not an iterator
In [20]: next(iter({1:1, 2:2}))
Out[20]: 1

In [20]: next(iter({1:1, 2:2}))
Out[20]: 1

[Copilot]

Pull request overview

This PR fixes a bug in the Expr class by removing an incorrectly implemented __next__ method. The class is designed to be an iterable (like a Python dict) rather than an iterator.

Changes:

• Removed the broken __next__ method from the Expr class that was attempting to call next() on a dict object

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