Allow Term objects as keys in Expr __getitem__

Updated Expr.__getitem__ to accept both Term and Expr instances as keys, improving flexibility when accessing children.

Author: Zeroto521

src/pyscipopt/expr.pxi

@@ -61,7 +61,7 @@ class Expr:
         return frozenset(self.children.items()).__hash__()
 
     def __getitem__(self, key):
-        if not isinstance(key, Expr):
+        if not isinstance(key, (Term, Expr)):
             key = Term(key)
         return self.children.get(key, 0.0)