Add PyZX-based ZX transformer to contrib (gh-6585)

cirq-core/cirq/contrib/__init__.py

@@ -24,3 +24,4 @@
 from cirq.contrib.qcircuit import circuit_to_latex_using_qcircuit as circuit_to_latex_using_qcircuit
 from cirq.contrib import json  # noqa: F401
 from cirq.contrib.circuitdag import CircuitDag as CircuitDag, Unique as Unique
+from cirq.contrib.zxtransformer import zx_transformer as zx_transformer

cirq-core/cirq/contrib/requirements.txt

@@ -6,3 +6,6 @@ pylatex~=1.4
 # quimb
 quimb~=1.8
 opt_einsum
+
+# zxtransformer
+pyzx>=0.10.0

cirq-core/cirq/contrib/zxtransformer/__init__.py

@@ -0,0 +1,22 @@
+# Copyright 2024 The Cirq Developers
+#
+# 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
+#
+#     https://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.
+
+"""ZX-calculus circuit optimization via PyZX (requires the ``pyzx`` package)."""
+
+from cirq.contrib.zxtransformer.zxtransformer import (
+    ZXTransformer as ZXTransformer,
+    cirq_gate_to_zx_gate as cirq_gate_to_zx_gate,
+    full_reduce as full_reduce,
+    zx_transformer as zx_transformer,
+)