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

pyproject.toml

@@ -13,8 +13,8 @@ dependencies = [
 license = "WTFPL"
 
 [project.scripts]
-zon2json = "zig_fetch_py.main:main"
 zig-fetch = "zig_fetch_py.__main__:main"
+zon2json = "zig_fetch_py.__main__:zon2json"
 
 [build-system]
 requires = ["hatchling"]