Be stricter on some class properties accessors.

[LoicPoullain]

Issue

Some class properties have should be readonly

Solution and steps

• [x] Update the classes.

Breaking changes

Context.request, Context.state, HttpResponse.statusCode, HttpResponse.statusMessage, WebsocketContext.socket and WebsocketContext.state are readonly.

Checklist

• [x] Add/update/check docs (code comments and docs/ folder).
• [x] Add/update/check tests.
• [x] Update/check the cli generators.