Add layout downloading port option

[httphypixelnet]

This PR aims to fix #246, giving users the option to use a custom port for the "Download from Robot" web server. I didn't actually add a unit test for that functionality specifically, but I integrated the preferences key into existing unit tests, and tested that it worked manually.

[codecov]

Codecov Report

❌ Patch coverage is 25.64103% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.90%. Comparing base (3673f6b) to head (2e2a251).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/pages/dashboard/dashboard_page_settings.dart	3.70%	26 Missing ⚠️
lib/widgets/settings_dialog.dart	62.50%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #345      +/-   ##
==========================================
- Coverage   78.12%   77.90%   -0.23%     
==========================================
  Files          93       93              
  Lines        9436     9473      +37     
==========================================
+ Hits         7372     7380       +8     
- Misses       2064     2093      +29     

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