Extend given to be used outside the current block

This does not work as expected

    it 'includes level 2 nested parameter within #declared(params)' do
      subject.params do
        requires :bar, type: Hash do
          optional :a

          optional :c, type: Hash do
            given :a do
              requires :b
            end
          end
        end
      end
      subject.get('/nested') { declared(params).to_json }
      get '/nested', bar: { a: true, c: { b: 'yes' } }
      expect(JSON.parse(last_response.body)).to eq('bar' => { 'a' => "true", 'b' => 'yes' })
    end

This is because given dsl already does the validation and only looks in the current block context. This could be changed so that given also looks in the parent blocks

Start by locating the parameter DSL implementation for given, requires, optional, and declared(params), then find the tests covering nested parameter validation. Reproduce the shown nested example and inspect how given resolves values in its current block. Done means the example passes with given :a reading the parent block value without breaking existing validation tests.