Add koa as peerDeps and fix the encoding option propagation

[3imed-jaberi]

Description

Fix #155 and #157

Checklist

• [x] I have ensured my pull request is not behind the main or master branch of the original repository.
• [x] I have rebased all commits where necessary so that reviewing this pull request can be done without having to merge it first.
• [x] I have written a commit message that passes commitlint linting.
• [x] I have ensured that my code changes pass linting tests.
• [x] I have ensured that my code changes pass unit tests.
• [x] I have described my pull request and the reasons for code changes along with context if necessary.

[titanism]

released https://github.com/koajs/bodyparser/releases/tag/v5.1.1

thank you @3imed-jaberi 🙏