feat: Mk:apiが失敗時エラー型の値を返すように (#2)

[FineArchs]

What

AiScriptのMk:api関数が失敗した時、エラー型の値（AiScript 0.16.0で追加）を返すようにします。

Why

#11839

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

Patch coverage has no change and project coverage change: +0.01% 🎉

Comparison is base (aa80cfd) 78.88% compared to head (4482feb) 78.89%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #11843      +/-   ##
===========================================
+ Coverage    78.88%   78.89%   +0.01%     
===========================================
  Files          924      175     -749     
  Lines        97523    22856   -74667     
  Branches      7748      511    -7237     
===========================================
- Hits         76927    18033   -58894     
+ Misses       20596     4823   -15773     

see 749 files with indirect coverage changes

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[syuilo]

🙏