Improve TypeScript Typing

[mshriner]

Addresses #2

• improve typescript typing
• resolve sonar(javascript:S2310)
• add xo badge to README
• upgrade testing dependencies

[fregante]

Thank you! 🙏

[mshriner]

@fregante Would you please run the workflows again for me? If they fail again I can try further downgrading those dev dependencies.

[mshriner]

Running xo locally produces a lot more errors than the GitHub Actions that just ran... I only fixed the ones the Actions version complained about.

[fregante]

Running xo locally produces a lot more errors than the GitHub Actions that just ran

Not for me, it's more likely that your npm install failed or you're not using the right node version. But it's ok, thank you for the PR and sorry for the long review time!