fix: Move json import to module level in tests

Per Copilot review, import statements should be at the module level for
consistency and readability. Moved all 'import json' statements from inside
test functions to the top of test_api.py.

- Added 'import json' to module imports (line 13)
- Removed 3 inline imports from test functions
- All tests still passing (11/11)
- Code quality checks pass (ruff, mypy)

Author: jreakin

tests/test_api.py

@@ -10,6 +10,8 @@
 Python type normalization is tested in test_normalization.py.
 """
 
+import json
+
 import pytest
 
 from toon_format import ToonDecodeError, decode, encode
@@ -297,9 +299,6 @@ def test_decode_with_json_indent_returns_string(self):
         options = DecodeOptions(json_indent=2)
         result = decode(toon, options)
         assert isinstance(result, str)
-        # Verify it's valid JSON
-        import json
-
         parsed = json.loads(result)
         assert parsed == {"id": 123, "name": "Alice"}
 
@@ -351,8 +350,6 @@ def test_decode_json_indent_with_unicode(self):
         toon = 'name: "José"'
         result = decode(toon, DecodeOptions(json_indent=2))
         assert "José" in result
-        import json
-
         parsed = json.loads(result)
         assert parsed["name"] == "José"
 
@@ -375,8 +372,6 @@ def test_decode_json_indent_complex_nested(self):
   version: 1
   active: true"""
         result = decode(toon, DecodeOptions(json_indent=2))
-        import json
-
         parsed = json.loads(result)
         assert parsed["users"][0] == {"id": 1, "name": "Alice"}
         assert parsed["metadata"]["version"] == 1