Auto add nullable beans to auto-requires/Fix Proxy not writing @Nullable

[SentryMan]

So after all this autoRequires stuff, wouldn't it be easier to have avaje auto add nullable types to auto requires instead of
needing to manually define @InjectModule(requires={X,Y,Z}) for every single nullable bean?

• Adds a static set to ProcessingContext that we can use to keep track of nullable/optional types
• Update Field and Method Readers to add the bean type to the set when nullable or Optional Type is detected
• Fixes Proxy Writer not writing @Nullable annotations when needed

Fixes #244

[rbygrave]

I think this is going to be a nice improvement / less confusing for folks using nullable / optional. Good stuff!!