fix(vtk): transpose before numpy_to_vtk in add_vector

[wpbonelli]

add_vector() assigns a vector to each grid cell. The method takes an array of shape (3, nnodes) and passes it to numpy_support.numpy_to_vtk(), which due to the order of indices flattens it in column-major order, but VTK expects row-major order.

So where cell i should get

(x[i], y[i], z[i])

it instead gets

(x[3i], x[3i+1], x[3i+2])

Fixed by transposing the array passed to numpy_to_vtk() so it is (nnodes, 3) and is flattened/interpreted correctly

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 72.4%. Comparing base (556c088) to head (ec740f6).
⚠️ Report is 142 commits behind head on develop.

Files with missing lines	Patch %	Lines
flopy/export/vtk.py	0.0%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2733      +/-   ##
===========================================
+ Coverage     55.5%    72.4%   +16.9%     
===========================================
  Files          644      674      +30     
  Lines       124135   130618    +6483     
===========================================
+ Hits         68947    94650   +25703     
+ Misses       55188    35968   -19220     

Files with missing lines	Coverage Δ
flopy/export/vtk.py	69.8% <0.0%> (-8.3%)	⬇️

... and 569 files with indirect coverage changes

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