fix(altair): use round instead of int and update related test

Author: daizutabi

marimo/_output/formatters/altair_formatters.py

@@ -120,8 +120,8 @@ def _format_png_mimebundle(
         "image/png": data_url or "",
         METADATA_KEY: {
             "image/png": {
-                "width": int(metadata["width"]),
-                "height": int(metadata["height"]),
+                "width": round(metadata["width"]),
+                "height": round(metadata["height"]),
             }
         },
     }

tests/_output/formatters/test_altair_formatters.py

@@ -190,7 +190,7 @@ def test_altair_formatter_png():
         "_repr_mimebundle_",
         return_value=(
             {"image/png": b"png"},
-            {"image/png": {"width": 10, "height": 20}},
+            {"image/png": {"width": 10.2, "height": 19.8}},
         ),
     ):
         formatter = get_formatter(mock_chart)