fix(yaml): always use pure-Python ruamel.yaml

Resolves #55.

src/remarshal/main.py

@@ -510,7 +510,7 @@ def _decode_toml(input_data: bytes) -> Document:
 
 def _decode_yaml(input_data: bytes) -> Document:
     try:
-        yaml = ruamel.yaml.YAML(typ="safe")
+        yaml = ruamel.yaml.YAML(pure=True, typ="safe")
         doc = yaml.load(input_data)
 
         return cast(Document, doc)
@@ -742,7 +742,7 @@ def _encode_yaml(
     style: YAMLStyle,
     width: int,
 ) -> str:
-    yaml = ruamel.yaml.YAML()
+    yaml = ruamel.yaml.YAML(pure=True)
     yaml.default_flow_style = False
 
     yaml.default_style = style  # type: ignore

tests/colon.json

@@ -0,0 +1 @@
+{"data":[{"src":{"url":"http://example.com"}}]}

tests/colon.yaml

@@ -0,0 +1,2 @@
+data:
+  - src: {url: http://example.com}

tests/test_remarshal.py

@@ -643,6 +643,15 @@ def test_yaml2toml_timestamp_key(self, convert_and_read) -> None:
         reference = read_file("timestamp-key.toml")
         assert output == reference
 
+    def test_yaml_colon(self, convert_and_read) -> None:
+        output = convert_and_read(
+            "colon.yaml",
+            "yaml",
+            "json",
+        )
+        reference = read_file("colon.json")
+        assert output == reference
+
     def test_yaml_width_default(self, convert_and_read) -> None:
         output = convert_and_read(
             "long-line.json",