Fix failing local Windows tests due to ruamel parsing (#3275)

Update multianimal project fixture to produce stable YAML: import ruamel.yaml.scalarstring.SingleQuotedScalarString and use it for the video_sets key (posix path), set yaml width to avoid unwanted wrapping, and use project_dir.as_posix() for project_path. Also write config.yaml with explicit UTF-8 encoding and ensure crop is a string. These changes make YAML dumping deterministic and platform-independent for the test.