fix: fix CONTRIBUTING.md placeholders, bare except clauses, and add convert.py tests (#3485) [skip ci]

* docs: fix codestyle placeholders in CONTRIBUTING.md

Replace unresolved {codestyle} and {URLofCodestyle} template
variables with Ruff, the project's actual linter/formatter
as configured in .pre-commit-config.yaml.

* fix: replace bare except clauses with specific exception types

- quantization.py: use except ImportError for optional torchao imports
  (consistent with line 48 which already uses ImportError correctly)
- cli/config.py: use except (RuntimeError, AssertionError) for CUDA
  device property query

Prevents masking unrelated errors like KeyboardInterrupt or SystemExit.

* test: add unit tests for convert.py JSON/JSONL utilities

Cover FileReader, FileWriter, StdoutWriter, JsonParser,
JsonlSerializer, and JsonToJsonlConverter with 8 test cases
including roundtrip and edge case (empty list) scenarios.

Previously this module had zero test coverage.

* fix: address CodeRabbit review feedback

- quantization.py: catch (ImportError, RuntimeError) for optional
  torchao imports; CUDA wheel/GPU mismatches raise RuntimeError,
  not ImportError
- convert.py: remove unused output_file_path parameter from
  JsonToJsonlConverter.convert() — FileWriter already holds the
  output path from construction
- tests/test_convert.py: update call site to match new signature

tests/test_convert.py

@@ -0,0 +1,91 @@
+"""Unit tests for src/axolotl/convert.py"""
+
+import json
+
+import pytest
+
+from axolotl.convert import (
+    FileReader,
+    FileWriter,
+    JsonlSerializer,
+    JsonParser,
+    JsonToJsonlConverter,
+    StdoutWriter,
+)
+
+
+class TestJsonParser:
+    def test_parse_valid_json_array(self):
+        parser = JsonParser()
+        result = parser.parse('[{"key": "value"}]')
+        assert result == [{"key": "value"}]
+
+    def test_parse_valid_json_object(self):
+        parser = JsonParser()
+        result = parser.parse('{"key": "value"}')
+        assert result == {"key": "value"}
+
+    def test_parse_invalid_json_raises(self):
+        parser = JsonParser()
+        with pytest.raises(json.JSONDecodeError):
+            parser.parse("not valid json")
+
+
+class TestJsonlSerializer:
+    def test_serialize_single_item(self):
+        serializer = JsonlSerializer()
+        result = serializer.serialize([{"a": 1}])
+        assert result == '{"a": 1}'
+
+    def test_serialize_multiple_items(self):
+        serializer = JsonlSerializer()
+        result = serializer.serialize([{"a": 1}, {"b": 2}])
+        lines = result.split("\n")
+        assert len(lines) == 2
+        assert json.loads(lines[0]) == {"a": 1}
+        assert json.loads(lines[1]) == {"b": 2}
+
+    def test_serialize_empty_list(self):
+        serializer = JsonlSerializer()
+        result = serializer.serialize([])
+        assert result == ""
+
+
+class TestFileReaderWriter:
+    def test_read_write_roundtrip(self, tmp_path):
+        test_file = tmp_path / "test.txt"
+        content = '{"hello": "world"}'
+        writer = FileWriter(str(test_file))
+        writer.write(content)
+
+        reader = FileReader()
+        result = reader.read(str(test_file))
+        assert result == content
+
+
+class TestStdoutWriter:
+    def test_write_to_stdout(self, capsys):
+        writer = StdoutWriter()
+        writer.write("hello")
+        captured = capsys.readouterr()
+        assert captured.out == "hello\n"
+
+
+class TestJsonToJsonlConverter:
+    def test_convert_json_to_jsonl(self, tmp_path):
+        input_data = [{"name": "Alice"}, {"name": "Bob"}]
+        input_file = tmp_path / "input.json"
+        output_file = tmp_path / "output.jsonl"
+
+        input_file.write_text(json.dumps(input_data), encoding="utf-8")
+
+        converter = JsonToJsonlConverter(
+            FileReader(), FileWriter(str(output_file)), JsonParser(), JsonlSerializer()
+        )
+        converter.convert(str(input_file))
+
+        result = output_file.read_text(encoding="utf-8")
+        lines = result.split("\n")
+        assert len(lines) == 2
+        assert json.loads(lines[0]) == {"name": "Alice"}
+        assert json.loads(lines[1]) == {"name": "Bob"}