Bug Fix: Asset table operations

[ejsimley]

This small pull request fixes a few issues I found when calling the get_freestream_turbines method in PlantData and running wake loss analyses for a wind plant with both turbine and tower assets.

1. In calculate_asset_distance_matrix and calculate_asset_direction_matrix, the diagonals of the matrices weren't getting set to np.inf like we expected. This could possibly be because of a new pandas version.
2. An error would appear in get_freestream_turbines when there are tower assets in addition to turbine assets. Specifically, self.asset.index includes both turbine and tower indices, but freestream_indices only includes boolean values corresponding to turbines, so the dimensions didn't match in the return statement.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.49%. Comparing base (94fd51f) to head (12d489e).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #282      +/-   ##
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+ Coverage    72.46%   72.49%   +0.02%     
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  Files           29       29              
  Lines         3683     3687       +4     
  Branches       794      794              
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+ Hits          2669     2673       +4     
  Misses         825      825              
  Partials       189      189              

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[RHammond2]

Thanks for catching this, @ejsimley! This fix looks good to me.