Agent shutdown may block on an extra network call

- add an option to not flush last profiling snapshot
- add an option to not wait for session upload thread to finish

Start by tracing the agent shutdown path, including the final profiling snapshot flush and the session upload thread. Identify where shutdown waits on these operations, then verify that each new option prevents its corresponding work and that shutdown no longer makes the extra network call when both are disabled.

索引モデルが issue の本文から書いたものです。