Refactor CLI and consolidate ZON conversion functionality

- Move `zon2json` command from `main.py` to `__main__.py`
- Create shared `convert_zon_to_json` function for consistent JSON conversion
- Update pyproject.toml to point `zon2json` script to new location
- Update README with `uv run` prefix for CLI commands
- Expose key functions in `__init__.py` for easier importing
- Remove redundant `main.py` file

zig_fetch_py/__init__.py

@@ -3,3 +3,8 @@ zig-fetch-py - A tool to parse Zig Object Notation (ZON) files and convert them
 """
 
 __version__ = "0.1.0"
+
+from zig_fetch_py.parser import parse_zon_file, zon_to_json
+from zig_fetch_py.downloader import process_dependencies, get_cache_dir
+
+__all__ = ["parse_zon_file", "zon_to_json", "process_dependencies", "get_cache_dir"]