feat: add hybrid commands

[AstreaTSS]

What type of pull request is this?

• [x] Non-breaking code change
• [ ] Breaking code change
• [x] Documentation change/addition
• [ ] Tests change

Description

This PR adds hybrid commands, which allow using a slash command as a prefixed command too. Efforts have been taken to make sure the resulting prefixed command is as close to the slash command as possible.

This PR also, mostly by consequence:

• Adds in HybridContext. An argument has been added to Client to allow setting a custom subclass of HybridContext, too.
• Allows using custom signatures for prefixed commands. This is a very low level thing and should only be manipulated by those who know what they're doing.
• Changes prefixed commands to base if it should use a kwarg for a parameter or not based on its parameter type instead of blindly guessing.
• Adds kind to PrefixedCommandParameter.
• Adds docs for hybrid commands.

Due to the many, many ways slash commands can be declared, there may be some bugs that I missed (though I did test a number of combinations and options).

Changes

See above. Usually, I would type something out, but I feel like this would be a repeat of the description if I bothered.

Checklist

• [x] I've formatted my code with Black
• [x] I've ensured my code works on Python 3.10.x
• [x] I've tested my code

[silasary]

Can you go into tests/test_protocols.py and a check that Hybrid contexts are SendableContexts?

[AstreaTSS]

Done!

[LordOfPolls]

Due to the scope of this PR it should not be merged until we have at least a second trust-worthy reviewer

That said if it hits 14 days since my review without a second, it'll be merged

[AstreaTSS]

Found a little oversight - min/max_length wasn't being respected. That's been fixed with the latest two commits.