Prevent duplicate option names

[cllns]

Describe the bug

dry-cli allows one to define duplicate options that override each other. However, the all show up when running --help.

While in a single class this is easy to avoid, when building many commands and sharing behavior, it's easy to accidentally include extra options. See: hanami/cli#278

To Reproduce

In test.rb:

require "dry/cli"

module Foo
  module CLI
    module Commands
      extend Dry::CLI::Registry

      class Request < Dry::CLI::Command
        option :mode, default: "http", values: %w[http http2]
        option :mode, default: "foo", values: %w[bar baz]

        def call(**options) = puts "Performing a request (mode: #{options.fetch(:mode)})"
      end

      register "request", Request
    end
  end
end

Dry::CLI.new(Foo::CLI::Commands).call

Then

# ruby test.rb request --help
Command:
  test.rb request

Usage:
  test.rb request

Options:
  --mode=VALUE                      # : (http/http2), default: "http"
  --mode=VALUE                      # : (bar/baz), default: "foo"
  --help, -h                        # Print this help

It shows both --modes. Same thing happens if they're identical, too.

Expected behavior

I would expect either:

1. The second option to override the first one and completely remove the first one from --help (since this is what actually happens when you try to execute it with that option. only bar/baz are valid, not http/http2.
2. An error to be raised, saying it's not allowed

My environment

Ruby 3.3, dry-cli 1.2.0 (latest as of writing this)