[MNT] raise plotly bound to plotly<7 to support plotly 6.X (#632)

This PR enables support for plotly 6.

Author: ms32035

pyproject.toml

@@ -55,7 +55,7 @@ all_extras = [
     "plotly>=5.0.0,<6",
     "scikit-learn>=0.24.1",
     "ecos>=2.0.14,<2.1",
-    "plotly>=5.0.0,<6",
+    "plotly>=5.0.0,<7",
     "cvxopt; python_version < '3.14'",
 ]