Ensure websocket handler types are only applied to websocket handlers

[airhorns]

This corrects an issue introduced in #64 where upon adding fastify-websocket to a project all route handlers were (accidentally) assumed to be websocket handlers getting the different (and decidedly less useful) types. My bad! This corrects the issue by using a type-land overload of the RouteShorthand function definition to change the type of the handler only if the handler is in fact { websocket: true }.

Also adds tests, tsd is handy!

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows Code of conduct

[airhorns]

Please hold off on merging this I am fighting with another issue that might be relevant ... TBD

[mcollina]

lgtm

[airhorns]

Ok -- this is good to go. Developing these types is real tricky because all the types across all the transitive dependencies have to agree exactly. My issue was that transitive dependencies in my project were including older types and when npm linking it gets even crazier. yalc helped a lot with this and I feel good that this is working now!

[mcollina]

Nice job! yalc seems very useful, I did not know it!