fix: properly parse image from dict for embeds

[AstreaTSS]

Pull Request Type

• Feature addition
• Bugfix
• Documentation update
• Code refactor
• Tests improvement
• CI/CD pipeline enhancement
• Other: [Replace with a description]

Description

Ever since the change to make Embed have images instead of image, it seems like there was a bug where embeds from messages (or from a passed-in dictionary in general) were not processed properly by Embed and so were missing from the resulting object. This PR fixes that.

Changes

• Convert "image" field in a dict to "images" if detected when processing the dict for Embed.

Related Issues

Test Scenarios

• Send message on Discord with an embed with an image.
• Fetch that message, look at the embed, and observe the lack of an image in the resulting object.

Python Compatibility

• I've ensured my code works on Python 3.10.x
• I've ensured my code works on Python 3.11.x

Checklist

• I've run the pre-commit code linter over all edited files
• I've tested my changes on supported Python versions
• I've added tests for my code, if applicable
• I've updated / added documentation, where applicable