feat: prepare koa-mount to v5.0.0

[3imed-jaberi]

Checklist

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

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Achived for v5.0.0

• Migrate from Travis CI to GitHub Actions
• Support Node.js v18+
• Support Koa v3
• Migrate from 'debug' module to native Node.js
• Migrate from 'istanbul' to 'nyc'
• Upgrade all dependencies
• Replace pure 'eslint' with 'xo'
• Add husky
• Update .gitignore file
• Migrate callbacks to async/await style

[3imed-jaberi]

@jonathanong I just see your opened issue here , so I am not sure what the direction. We should continue supporting this module or not, especially have more than 150k weekly downloads?? Because I have a plan for v6 too by rewriting the module in typescript, using jest instead of mocha and publishing it under @koa/mount ...

[jonathanong]

we can debate removing support for mounting apps within each other as v7. we should definitely go the direction you are discussing though for v6.

[jonathanong]

if possible, can you split those tasks into separate PRs? at least the typescript change. no big deal if you don't though