feat: Bring back process_attributes callback for attribute processing

[joelmoss]

Just an experiment right now, but I really would like to bring this hook back, as I still have a big need for it, and it is the biggest blocker to me using Phlex 2.

Without this, I will have to create a fork, which I would really, really like to avoid.

More tests are needed against things like caching and the compiler, but this works. Also not benchmarked this at all.

Simple define a process_attributes method in your component(s). Example...

def process_attributes(attrs)
	attrs.tap do |it|
		it[:age] = 48 if it[:name] == 'Joel'
	end
end

Anyway, thoughts? Suggestions? Objections?