feat(text): Add Add and AddAssign implementations for Line, Span, and Text

[joshka]

This enables:

let line = Span::raw("Red").red() + Span::raw("blue").blue();
let line = Line::raw("Red").red() + Span::raw("blue").blue();
let line = Line::raw("Red").red() + Line::raw("Blue").blue();
let text = Line::raw("Red").red() + Line::raw("Blue").blue();
let text = Text::raw("Red").red() + Line::raw("Blue").blue();

let mut line = Line::raw("Red").red();
line += Span::raw("Blue").blue();

let mut text = Text::raw("Red").red();
text += Line::raw("Blue").blue();

line.extend(vec![Span::raw("1"), Span::raw("2"), Span::raw("3")]);

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.5%. Comparing base (6ce447c) to head (e2e2c0a).

Additional details and impacted files

@@          Coverage Diff           @@
##            main   #1236    +/-   ##
======================================
  Coverage   94.5%   94.5%            
======================================
  Files         65      65            
  Lines      15136   15260   +124     
======================================
+ Hits       14305   14429   +124     
  Misses       831     831            

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[kdheepak]

I like it! I am curious what others think though

[orhun]

very nice!