Fix PluginOptions incorrect typings

[felixputera]

Hello 👋

First of all, thanks @mcollina, @delvedor & all contributors for the awesome fastify ecosystem. I had just recently dived into it & I'm very impressed.

Moving on to the issue on hand, I found out that the TS typing provided for PluginOptions (used in fastify.register(ws, opts \*here*\) is incorrect: the typings requires both handler and options to be passed in. I looked into the docs & code to verify that it has defaults specified.

I fixed this in this PR, and had added tests to cover this use-case. Additionally, I did minor clean-up on the declaration file.

I think this addresses #47 too.

Checklist

• run npm run test and npm run benchmark (I couldn't find npm run bench nor npm run benchmark, should the PR template be updated?)
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows Code of conduct

[mcollina]

lgtm

[mcollina]

Thanks, I'm glad that you like it.

[Eomm]

💪🏻

[mcollina]

lgtm