Add Camera-Stream Crosshairs

[EmeraldWither]

Resolves #226.

Allows users to create a crosshair with an x, y, thickness, height, width, and color.

Todo:

• add relevant options in widget properties window to allow user to customize
• save options
• double check all tests and write new ones
• double check any possible performance impacts

[codecov]

Codecov Report

Attention: Patch coverage is 57.14286% with 69 lines in your changes missing coverage. Please review.

Project coverage is 78.03%. Comparing base (1032e94) to head (f3b8d8f).

Files with missing lines	Patch %	Lines
lib/widgets/mjpeg.dart	0.00%	47 Missing ⚠️
.../widgets/nt_widgets/multi_topic/camera_stream.dart	80.70%	22 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #260      +/-   ##
==========================================
- Coverage   78.36%   78.03%   -0.34%     
==========================================
  Files          86       86              
  Lines        8594     8749     +155     
==========================================
+ Hits         6735     6827      +92     
- Misses       1859     1922      +63     

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[EmeraldWither]

I am not going to lie, I am not quite sure how to test custom painters. From what I have seen online, the main way to do it is to have an image that has the specific overlay from the CustomPainter already done, and to then compare it pixel by pixel during the test.

[EmeraldWither]

Updated settings page