Add stimcirq tag conversions (#866)

- Add `tag: str = ""` to `stim.Circuit.append`
- Stim tags now become string tags on cirq circuit operations
- A string tag on a cirq operation will turn into a stim tag by default
if there is exactly one such string tag
- Add optional `tag_func` argument to
`stimcirq.cirq_circuit_to_stim_circuit`

Some inspiration from #862

doc/python_api_reference_vDev.md

@@ -831,6 +831,8 @@ def append(
     name: str,
     targets: Union[int, stim.GateTarget, Iterable[Union[int, stim.GateTarget]]],
     arg: Union[float, Iterable[float]],
+    *,
+    tag: str = "",
 ) -> None:
     pass
 @overload
@@ -844,6 +846,8 @@ def append(
     name: object,
     targets: object = (),
     arg: object = None,
+    *,
+    tag: str = '',
 ) -> None:
     """Appends an operation into the circuit.
 
@@ -894,6 +898,7 @@ def append(
             compatibility reasons, `cirq.append_operation` (but not
             `cirq.append`) will default to a single 0.0 argument for gates that
             take exactly one argument.
+        tag: A customizable string attached to the instruction.
     """
 ```
 

doc/stim.pyi

@@ -303,6 +303,8 @@ class Circuit:
         name: str,
         targets: Union[int, stim.GateTarget, Iterable[Union[int, stim.GateTarget]]],
         arg: Union[float, Iterable[float]],
+        *,
+        tag: str = "",
     ) -> None:
         pass
     @overload
@@ -316,6 +318,8 @@ class Circuit:
         name: object,
         targets: object = (),
         arg: object = None,
+        *,
+        tag: str = '',
     ) -> None:
         """Appends an operation into the circuit.
 
@@ -366,6 +370,7 @@ class Circuit:
                 compatibility reasons, `cirq.append_operation` (but not
                 `cirq.append`) will default to a single 0.0 argument for gates that
                 take exactly one argument.
+            tag: A customizable string attached to the instruction.
         """
     def append_from_stim_program_text(
         self,
@@ -398,6 +403,8 @@ class Circuit:
         name: object,
         targets: object = (),
         arg: object = None,
+        *,
+        tag: str = '',
     ) -> None:
         """[DEPRECATED] use stim.Circuit.append instead
         """