Function splinter_set 

pub unsafe extern "C" fn splinter_set(
    key: *const c_char,
    val: *const c_void,
    len: usize,
) -> c_int

@brief Sets or updates a key-value pair in the store. @param key The null-terminated key string. @param val Pointer to the value data. @param len The length of the value data. Must not exceed max_val_sz. @return 0 on success, -1 on failure (e.g., store is full).