minor type fixes(nanosec -> microsec)

* 그밖의 수정
** remove api namespace.
** fix typo.

Change-Id: I5020feea728e3b1fe9f943dae230bc9fecda4e2b
using fun::Uuid

Change-Id: I685a37fe0ea61df4d4d56f8f7eb9666afd409ed2
fun::string -> string

Change-Id: I0a8e9e94b5af046d72820bddb835565567e25fe6
minor lint fixes: const string -> const char *

Change-Id: Iecd25bef9a4f69d218fe9f22e49bf14e0aae8bbe
minor code clean-up.

Change-Id: Ia57d7f8cb04456771b09ffb634d848f7b13e5021