separate builders to another package (`@purplet/builders`), and also re-export/add other builders

[paperdave]

Two points:

• The docs mention ButtonBuilder, which isn't something we export. It's from @discordjs/builders.
• I would like to move purplet's src/builders folder into it's own package.

This potential package would either re-export useful builders like ButtonBuilder, or just re-implement them. I'm kind of siding on the re-implement side of things, especially since djs builders has 5 dependencies, while the builders we have made ourself only depend on discord-api-types.

Though, we probably would keep the util types OptionBuilderEntryTo* from OptionBuilder inside of purplet itself as those refer to other parts of purplet.

[Clembs]

Builders are now part of @purplet/utils, although not all of them are implemented (looking at ButtonBuilder and SelectMenuBuilder) but that will come soon, therefore this issue is closed because the package itself now exists.