betterproto: support Struct and Value (#551)

* betterproto: support `Struct` and `Value`

Signed-off-by: William Woodruff <william@trailofbits.com>

* betterproto: handle struct in to_dict as well

Signed-off-by: William Woodruff <william@trailofbits.com>

* tests: add Struct roundtrip tests

Signed-off-by: William Woodruff <william@trailofbits.com>

* specialize from_dict and to_dict on Struct

...rather than special-casing in the Message ABC.

Signed-off-by: William Woodruff <william@trailofbits.com>

* betterproto: `poe format`

Signed-off-by: William Woodruff <william@trailofbits.com>

* Update src/betterproto/__init__.py

Co-authored-by: James Hilton-Balfe <gobot1234yt@gmail.com>

* remove future annotations

Signed-off-by: William Woodruff <william@trailofbits.com>

* replace type[...] with typing.T

Signed-off-by: William Woodruff <william@trailofbits.com>

* quote instead

Signed-off-by: William Woodruff <william@trailofbits.com>

---------

Signed-off-by: William Woodruff <william@trailofbits.com>
Co-authored-by: James Hilton-Balfe <gobot1234yt@gmail.com>

Author: woodruffw

src/betterproto/lib/google/protobuf/__init__.py

@@ -0,0 +1,24 @@
+import json
+
+from betterproto.lib.google.protobuf import Struct
+
+
+def test_struct_roundtrip():
+    data = {
+        "foo": "bar",
+        "baz": None,
+        "quux": 123,
+        "zap": [1, {"two": 3}, "four"],
+    }
+    data_json = json.dumps(data)
+
+    struct_from_dict = Struct().from_dict(data)
+    assert struct_from_dict.fields == data
+    assert struct_from_dict.to_dict() == data
+    assert struct_from_dict.to_json() == data_json
+
+    struct_from_json = Struct().from_json(data_json)
+    assert struct_from_json.fields == data
+    assert struct_from_json.to_dict() == data
+    assert struct_from_json == struct_from_dict
+    assert struct_from_json.to_json() == data_json