fix: PID 1 問題のためのシグナルハンドラを追加

[MikuroXina]

Type of Change:

バグの修正

Details of implementation (実施内容)

PID 1 問題を解消するためのシグナルハンドラを追加し, Docker 上でこのプロセスをキルした場合でも正常に終了できるようにしました.

[codecov-commenter]

Codecov Report

Merging #640 (5302127) into main (53da704) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #640   +/-   ##
=======================================
  Coverage   73.89%   73.89%           
=======================================
  Files          64       64           
  Lines        4551     4551           
  Branches      410      410           
=======================================
  Hits         3363     3363           
  Misses        781      781           
  Partials      407      407           

Flag	Coverage Δ
unittests	73.89% <ø> (ø)

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