Fix margin

[Muscraft]

Margin was being utilized for a whole Message when it really should be per Snippet, since that is what is displayed together. Margin should also be calculated by annotate-snippets and not passed in, as we know how to figure everything out.

To fix these problems, this PR does the following:

• Grouped a Snippet's DisplayLines together into a DisplaySet so all lines to be rendered for a Snippet are kept together
• Made annotations be a field in DisplayLine, so they can reference information about the line. This will also help us in the future to be able to fold annotations into one line where possible, as well as other future rendering improvements
• Made it so that the Margin for each DisplaySet is created internally, allowing for better formatting
• Replaced the ability to pass in Margin with the ability to pass in only column_width, so users can easily specify it without setting all of Margin

Breaking changes:

• Margin is now private
• You can only pass in column_width and not all of Margin as we now handle it internally