refactor: use pathlib.Path instead of os.path

[b31ngd3v]

BUT I'm not adverse to having a bigger refactoring PR where you use pathlib throughout extractor (and possibly in the tests that handle file paths?). I just don't want this to wind up being like we did with requests where part of the code uses it and part does not for a really long time.

Originally posted by @terriko in #1696 (comment)

files that need refactoring:

• cve_bin_tool/extractor.py
• test/test_extractor.py
• test/test_requirements.py
• test/test_input_engine.py
• test/test_scanner.py
• test/test_cli.py
• test/test_sbom.py
• test/test_json.py
• test/test_file.py
• test/test_config.py
• test/test_merge.py
• test/test_strings.py
• test/test_language_scanner.py
• test/test_package_list_parser.py
• test/test_output_engine.py