Function pio_package_study_json 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pio_package_study_json(
    pkg: *const PioPackage,
    errbuf: *mut c_char,
    errlen: usize,
) -> *mut c_char

Return the package study block as JSON, or null when absent. The returned string is owned by the library; free it with pio_string_free.