Port VF2 to rustworkx-core

releasenotes/notes/vf2-core-ccfb903a5cfb34b1.yaml

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+---
+features:
+  - |
+    Graph isomorphism using VF2(++) is now supported in ``rustworkx-core``
+    for ``petgraph`` graph types ``StableGraph`` and ``Graph`` (it may also
+    work for ``GraphMap``, but this is not verified).
+    To use it, import ``rustworkx_core::isomorphism::vf2`` which provides
+    function :func:`.is_isomorphic` for isomorphism testing in addition to the
+    ``Vf2Algorithm`` struct, which can be used to iterate over valid
+    isomorphic matches of two graphs. It also provides traits ``EdgeMatcher``
+    and ``NodeMatcher``, which allow a user-provided implementation of
+    node and edge equality.

rustworkx-core/src/isomorphism/mod.rs

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+// Licensed under the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License. You may obtain
+// a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations
+// under the License.
+
+//! Module for graph isomorphism.
+
+pub mod vf2;