Arb fix/d2q9 pf velocity

[TravisMitchell]

this initial fix at least allows the d2q9 phase field model to be run with normal cases. There is a chance that very complex geometry may cause edge conditions (e.g. where a solid node has a normal direction that points to another solid) that may require the introduction of a new field in the future.

Note that use of nan makes failcheck require to be applied with a focus area.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (7a6f0e3) 36.55% compared to head (f05a11b) 38.09%.
Report is 19 commits behind head on unstable.

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable     #471      +/-   ##
============================================
+ Coverage     36.55%   38.09%   +1.54%     
============================================
  Files           182      185       +3     
  Lines          8112     8355     +243     
============================================
+ Hits           2965     3183     +218     
- Misses         5147     5172      +25     

Flag	Coverage Δ
d2q9	26.64% <ø> (ø)
d2q9_bc	23.41% <ø> (ø)
d2q9_kuper	24.19% <ø> (ø)
d3q27_PSM_NEBB	31.77% <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.