fix: preserve HTML tables in Outlook .msg conversion

[lavish0000]

Closes #1567

Summary

• prefer the Outlook HTML body streams when converting .msg files
• run HTML bodies through the existing HTML-to-Markdown path so tables stay tables
• fall back to the plain-text body when no HTML body is available
• add regression coverage for both the HTML-body and plain-text fallback paths

Testing

• hatch test tests/test_outlook_msg_converter.py 'tests/test_module_vectors.py::test_guess_stream_info[test_vector4]' 'tests/test_module_vectors.py::test_convert_local[test_vector4]' 'tests/test_module_vectors.py::test_convert_stream_with_hints[test_vector4]' 'tests/test_module_vectors.py::test_convert_stream_without_hints[test_vector4]' 'tests/test_module_vectors.py::test_convert_file_uri[test_vector4]' 'tests/test_module_vectors.py::test_convert_data_uri[test_vector4]'\n- uvx black --check packages/markitdown/src/markitdown/converters/_outlook_msg_converter.py packages/markitdown/tests/test_outlook_msg_converter.py\n- hatch run types:check src/markitdown/converters/_outlook_msg_converter.py tests/test_outlook_msg_converter.py