Fix: aiscriptディレクトリ内の型エラー解消と単体テスト

[takejohn]

What

/packages/frontend/src/scripts/aiscriptディレクトリ内の型エラーを解消し、単体テストを追加します。

Why

#15173 (comment)
まだ一部だけどテスト書いてたら多くなったので一休み

Additional info (optional)

Checklist

• Read the contribution guide
• Test working in a local environment
• (If needed) Add story of storybook
• (If needed) Update CHANGELOG.md
• (If possible) Add tests

[codecov]

Codecov Report

Attention: Patch coverage is 95.71429% with 6 lines in your changes missing coverage. Please review.

Project coverage is 20.06%. Comparing base (4120c9a) to head (95fecc6).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
packages/frontend/src/scripts/aiscript/ui.ts	95.23%	4 Missing ⚠️
packages/frontend/src/scripts/misskey-api.ts	77.77%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #15191       +/-   ##
============================================
- Coverage    39.93%   20.06%   -19.88%     
============================================
  Files         1563      729      -834     
  Lines       197977   104047    -93930     
  Branches      3633     1198     -2435     
============================================
- Hits         79065    20874    -58191     
+ Misses      118307    82621    -35686     
+ Partials       605      552       -53     

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[takejohn]

#15158 で追加されたMk:removeにもテストを追加