Add support for deep=True to cirq.synchronize_terminal_measurements…

… transformer (#5118)

- Adds support to recursively run `cirq.synchronize_terminal_measurements` transformer on circuits wrapped inside a circuit operation by setting deep=True in transformer context.
- Part of #5039

cirq-core/cirq/transformers/synchronize_terminal_measurements.py

@@ -58,7 +58,7 @@ def find_terminal_measurements(
     return terminal_measurements
 
 
-@transformer_api.transformer
+@transformer_api.transformer(add_deep_support=True)
 def synchronize_terminal_measurements(
     circuit: 'cirq.AbstractCircuit',
     *,

cirq-core/cirq/transformers/synchronize_terminal_measurements_test.py

@@ -18,17 +18,35 @@
 
 
 def assert_optimizes(before, after, measure_only_moment=True, with_context=False):
-    transformed_circuit = (
-        cirq.synchronize_terminal_measurements(before, after_other_operations=measure_only_moment)
-        if not with_context
-        else cirq.synchronize_terminal_measurements(
-            before,
-            context=cirq.TransformerContext(tags_to_ignore=(NO_COMPILE_TAG,)),
-            after_other_operations=measure_only_moment,
-        )
+    context = cirq.TransformerContext(tags_to_ignore=(NO_COMPILE_TAG,)) if with_context else None
+    transformed_circuit = cirq.synchronize_terminal_measurements(
+        before, context=context, after_other_operations=measure_only_moment
     )
     cirq.testing.assert_same_circuits(transformed_circuit, after)
 
+    # Test nested circuit ops.
+    context = cirq.TransformerContext(
+        tags_to_ignore=("ignore",) + tuple([NO_COMPILE_TAG] if with_context else []), deep=True
+    )
+    c_nested = cirq.Circuit(
+        before,
+        cirq.CircuitOperation(before.freeze()).repeat(5).with_tags("ignore"),
+        before,
+        cirq.CircuitOperation(before.freeze()).repeat(6).with_tags("preserve_tag"),
+        before,
+    )
+    c_expected = cirq.Circuit(
+        before,
+        cirq.CircuitOperation(before.freeze()).repeat(5).with_tags("ignore"),
+        before,
+        cirq.CircuitOperation(after.freeze()).repeat(6).with_tags("preserve_tag"),
+        after,
+    )
+    transformed_circuit = cirq.synchronize_terminal_measurements(
+        c_nested, context=context, after_other_operations=measure_only_moment
+    )
+    cirq.testing.assert_same_circuits(transformed_circuit, c_expected)
+
 
 def test_no_move():
     q1 = cirq.NamedQubit('q1')