#169 Upgrade Mistune to v3

[kalbfled]

Description

These changes upgrade Mistune to v3.0.2, simplify the class inheritance structure, remove unused code, implement new unit tests, and bump the minor version number. Please begin by reading this comment that summarizes the task at a high level.

This comment summarizes the changes I made to the class structures.

• Mistune docs

issue #169

How Has This Been Tested?

I created an API branch that includes the changes on this Utils branch.

The API sends e-mail with both the html and plain text body (see here), and the mail client displays one. You can toggle which one in a client. You can also "view source" for the message, copy the base64 encoded html or plain text body, and view it decoded on a site like base64decode.

There is a template that contains every markdown element. We used this template for our test e-mails.

• Sent e-mail notifications from Prod and from Dev with Dev using these changes. Manually inspected for differences.
  • html
  • plain text
• Verified that "bulleted list" content continues to work (see below)
• Verified that SMS message are not affected (using the Comp & Pen template)

HTML with my changes looks identical to Prod

Plain text with my changes looks identical to Prod

"Bulletted list" content with my changes looks identical to Prod

Checklist

• I have assigned myself to this PR
• PR has an appropriate title: #9999 - What the thing does
• PR has a detailed description, including links to specific documentation
• I have added the appropriate labels to the PR.
• I did not remove any parts of the template, such as checkboxes even if they are not used
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to any documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works. Testing guidelines
• I have ensured the latest main is merged into my branch and all checks are green prior to review
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• The ticket was moved into the DEV test column when I began testing this change

[kalbfled]

This replaces the "take" functionality.