feat: add __bool__ to Embed

[AstreaTSS]

What type of pull request is this?

• Non-breaking code change
• Breaking code change
• Documentation change/addition
• Tests change

Description

This PR simply adds __bool__ to embed. This allows values like image to affect the output.
This also allows embeds with no "text" to be sent, as the embed would otherwise be evaluated as False during the sanity check instead.

Why? Guessing __len__ messed things up.

Changes

• I mean, literally what the title says.
  • From really basic experimentation, these fields, if present, allow the embed to be sent without Discord throwing an error. Any field that resulted in an error was left out.
  • Of course, I couldn't test video, but it's a good guess on my part.

Checklist

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