Add comment directive

[jeremiahlukus]

https://www.chordpro.org/chordpro/directives-comment/

All comments should be in the format {comment: Repeat}

Account to the chord prod format it should be italic and smaller by default.

I also added ChordLyricsLine tests since its has logic inside of it.

If you merge this Please squash to one commit I was watching TV while doing this ha.

Here is a pic of the lyrics and the song rendering.

[jeremiahlukus]

I also added a trim in all the model methods I feel like this should be included.

I removed flutter format in the workflow and replaced with dart format since this is the recommend way now.

[jeremiahlukus]

@paurakhsharma Let me know if this is a wanted change or not. If not then ill publish a fork so im not pulling from git.

[paurakhsharma]

@jeremiahlukus Thank you so much for the contribution. I'll have a look at it tonight and merge it.

[paurakhsharma]

Looks great, thank you for your contribution.