Allow guild & global slash commands with same name

[priyanuj-gogoi]

Describe the bug

Throws CommandRegistrationError when trying to create a guild & a global slash command having same name.

To Reproduce

1. Create a guild & a global slash command with same name.

   final globalSlash = ChatCommand(
    'slash', // Same name as "guildSlash"
    'placeholder',
    id(...)
   );
   
   final guildSlash = ChatCommand(
    'slash', // Same name as "globalSlash"
    'placeholder',
    singleChecks: [GuildCheck.id(...)],
    id(...)
   );

2. Add them in your client's CommandsPlugin().

   final commands = CommandsPlugin(...)
    ..addCommand(globalSlash)
    ..addCommand(guildSlash);

3. Run the bot & you'll get this error.

   Command with name "slash" already exists

Expected behavior

Perform the below curl command & then, check your bot slash commands. You'll see 2 slash commands having same name slash. Here, one is guild & the other one is global. This is what we want i.e to create guild & global slash commands with same name in nyxx_commands.

curl 'https://discord.com/api/v10/applications/BOT_ID/{guilds/GUILD_ID/,}commands' \
  -H 'Content-Type: application/json' -H 'Authorization: Bot TOKEN' \
  -d '{"name": "slash", "description": "placeholder"}'

[!IMPORTANT] When performing the above request, do replace BOT_ID, GUILD_ID & TOKEN with actual values.

Desktop:

• OS: Android
• Dart version: 3.1.5
• Nyxx version: 6.0.0 (GitHub dev branch)
• nyxx_commands version: 6.0.0 (GitHub main branch)

[abitofevrything]

Just had a look at this, and it's more complicated that it might first seem.

These are the two big issues:

• A command isn't necessarily bound to a single guild. It can be bound to multiple (GuildCheck.anyId([1, 2, 3])), which can then lead to overlaps with other commands: command A with guilds 1, 2 and 3 conflicts with command B with guild 2. This complicates the detection algorithm quite a bit.
• When using text commands, it's unclear whether !test in guild 1 should run the global !test or the guild !test.

I think the best solution would be to disallow this. It is supported by Discord, but I don't think it's great for UX and it's ambiguous how nyxx_commands should handle it.