[National Highways] Per-area destination handling.

[dracos]

Fixes https://github.com/mysociety/societyworks/issues/4477 [skip changelog]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.64%. Comparing base (f573cf6) to head (17f9a78).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5134      +/-   ##
==========================================
- Coverage   82.65%   82.64%   -0.01%     
==========================================
  Files         404      404              
  Lines       31499    31500       +1     
  Branches     4993     4993              
==========================================
  Hits        26034    26034              
- Misses       3982     3983       +1     
  Partials     1483     1483              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.