Translator: Improve test_image_translator to use temp_path instead of real path and add tests for markdown translator

[skytin1004]

Purpose

• This update refactors test_image_translator to use a temporary path instead of a real file path, which improves test reliability by isolating test output.

• Added new tests for markdown_translator

Description

• Updated ImageTranslator tests to utilize tmp_path fixture for temporary directories in place of hardcoded paths.
• Enhanced test_translate_image to assert the correct temporary path for translated images, improving isolation and ensuring that temporary data is used during test execution.
• Added new tests for markdown_translator.

Related Issue

#15

Does this introduce a breaking change?

• Yes
• No

Type of change

• Bugfix
• Feature
• Code style update (e.g., formatting, local variables)
• Refactoring (no functional or API changes)
• Documentation content changes
• Other... Please describe:

Checklist

Before submitting your pull request, please confirm the following:

• I have thoroughly tested my changes: I confirm that I have run the code and manually tested all affected areas.
• All existing tests pass: I have run all tests and confirmed that nothing is broken.
• I have added new tests (if applicable): I have written tests that cover the new functionality introduced by my code changes.
• I have followed the Co-op Translators coding conventions: My code adheres to the style guide and coding conventions outlined in the repository.
• I have documented my changes (if applicable): I have updated the documentation to reflect the changes where necessary.

Additional context

[skytin1004]

I have reviewed the changes and everything looks good.