Apply a little consistency to TestInstances.
Apply a little consistency to TestInstances.

- Consistent naming: generators are plural, arbitrary is a prefix.
- lazy to avoid initialization order fiascos.

aeons/http4s,hvesalai/http4s,aeons/http4s,m4dc4p/http4s,ZizhengTai/http4s,aeons/http4s,m4dc4p/http4s,hvesalai/http4s,rossabaker/http4s,ZizhengTai/http4s,reactormonk/http4s,reactormonk/http4s,m4dc4p/http4s,reactormonk/http4s,ZizhengTai/http4s,ChristopherDavenport/http4s,ChristopherDavenport/http4s,hvesalai/http4s,http4s/http4s,ChristopherDavenport/http4s,rossabaker/http4s