refactor(configuration): use node[attr] in node_missing_parameters?

[erimicel]

Replaces node.send(:[], attr) with node[attr] in Configuration#node_missing_parameters?. node is a Hash, so the behaviour is the same with less indirection. Split out from #60.

%i[protocol host port].any? { |attr| node.send(:[], attr).nil? }
# →
%i[protocol host port].any? { |attr| node[attr].nil? }

Verification

• bundle exec rspec spec/typesense/configuration_spec.rb: 5 examples, 0 failures. These include the missing protocol/host/port cases.
• bundle exec rubocop lib/typesense/configuration.rb: no offenses.

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