feat(Colour): factory method for #RRGGBB color codes

[Enegg]

Summary

This PR adds a new factory method .from_hex to disnake.Colour which accepts strings in the form of "#RRGGBB".
This is particularly useful in code editors that provide a color picker when they detect a color code.

Checklist

• If code changes were made, then they have been tested
  • I have updated the documentation to reflect the changes
  • I have formatted the code properly by running uv run nox -s lint
  • I have type-checked the code by running uv run nox -s pyright
• This PR fixes an issue
• This PR adds something new (e.g. new method or parameters)
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)

[shiftinv]

ext.commands.ColourConverter also handles hex colors of various formats, it could probably make use of this new method too.

[Enegg]

ext.commands.ColourConverter also handles hex colors of various formats, it could probably make use of this new method too.

I did expect there being a converter for this, but I'm not convinced this simple method is going to be of much use to it.

I can see these two relevant methods:

disnake/disnake/ext/commands/converter.py

Lines 705 to 714 in 9ebc9de

	def parse_hex_number(self, argument: str) -> disnake.Color:
	arg = "".join(i * 2 for i in argument) if len(argument) == 3 else argument
	try:
	value = int(arg, base=16)
	if not (0 <= value <= 0xFFFFFF):
	raise BadColourArgument(argument)
	except ValueError:
	raise BadColourArgument(argument) from None
	else:
	return disnake.Color(value=value)

disnake/disnake/ext/commands/converter.py

Lines 738 to 757 in 9ebc9de

	async def convert(self, ctx: AnyContext, argument: str) -> disnake.Color:
	if argument[0] == "#":
	return self.parse_hex_number(argument[1:])
	if argument[0:2] == "0x":
	rest = argument[2:]
	# Legacy backwards compatible syntax
	if rest.startswith("#"):
	return self.parse_hex_number(rest[1:])
	return self.parse_hex_number(rest)
	arg = argument.lower()
	if arg[0:3] == "rgb":
	return self.parse_rgb(arg)
	arg = arg.replace(" ", "_")
	method = getattr(disnake.Colour, arg, None)
	if arg.startswith("from_") or method is None or not inspect.ismethod(method):
	raise BadColourArgument(arg)
	return method()

...but they perform work/validation that goes beyond simply stripping the leading # and parsing as base 16. It also seems to support 3-digit #RGB format.