Function load_chipzen_config 

pub fn load_chipzen_config(
    search: Option<&[PathBuf]>,
) -> Result<Option<ChipzenConfig>, Error>

Discover and parse a chipzen.toml from the search path.

Pass Some(paths) to override the default search order. Returns Ok(None) if no file exists (NOT an error — the SDK falls back to explicit arguments). Returns Error::Protocol if a file is found but is malformed or lacks the [external_api] section — a “found but unusable” file is always a hard error so a typo surfaces immediately rather than being silently masked.