ngr: Add as dedicated install extra, pip install pueblo[ngr]

[amotl]

What the title says.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.49%. Comparing base (774bc77) to head (72be215).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #145      +/-   ##
==========================================
+ Coverage   85.12%   86.49%   +1.36%     
==========================================
  Files          26       26              
  Lines        1022     1022              
==========================================
+ Hits          870      884      +14     
+ Misses        152      138      -14     

Flag	Coverage Δ
main	62.91% <ø> (ø)
ngr	51.27% <ø> (ø)
sfa-full	40.11% <ø> (?)
sfa-minimal	38.35% <ø> (ø)
snippet	29.54% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

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