code: def chain_head(self):
          
          (vec_ptr, vec_len, vec_cap) = ffi.prepare_vec_result()
  
          try:
              _libexec(
                  'commit_store_get_chain_head',
                  self.pointer,
                  ctypes.byref(vec_ptr),
                  ctypes.byref(vec_len),
                  ctypes.byref(vec_cap))
          except ValueError:
              return None
  
          return self.deserialize_block(
              ffi.from_rust_vec(vec_ptr, vec_len, vec_cap))
docs: Return the head block of the current chain.