Fix/data array names

[tomalrussell]

Targets #321 and #316 which are slightly subtle around how Specs are matched in model/scenario dependencies - the pair of Specs must be equal up to name, but we do want to allow matched outputs and inputs to have different names.

DataHandle.get_data:

• must return a DataArray whose name matches the name of the input requested
• reads model results from the Store using the source output spec
• reads scenario variant data from the Store using the scenario provides spec
• may need to change the name on the DataArray returned from the Store to match the input name

[codecov[bot]]

Codecov Report

Merging #322 into master will increase coverage by 0.05%. The diff coverage is 93.75%.

@@            Coverage Diff             @@
##           master     #322      +/-   ##
==========================================
+ Coverage   69.75%   69.81%   +0.05%     
==========================================
  Files          59       59              
  Lines        5045     5055      +10     
  Branches      605      605              
==========================================
+ Hits         3519     3529      +10     
  Misses       1431     1431              
  Partials       95       95

Flag	Coverage Δ
#javascript	69.81% <93.75%> (+0.05%)	:arrow_up:
#python	77.79% <93.75%> (+0.05%)	:arrow_up:

Impacted Files	Coverage Δ
src/smif/data_layer/file/file_data_store.py	86.85% <ø> (ø)	:arrow_up:
src/smif/metadata/spec.py	99.1% <100%> (+0.01%)	:arrow_up:
src/smif/data_layer/data_handle.py	83.05% <100%> (+0.44%)	:arrow_up:
src/smif/data_layer/data_array.py	83.87% <66.66%> (+0.26%)	:arrow_up:

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[tomalrussell]

Yes, let's document this more explicity. I think it's the common case that the output/input pair in a dependency will be named the same, so should be an easy recommendation.

Yes, after this PR, the store returns the data as originally named, then the data handle changes the name to what's expected by whoever called DataHandle.get_data (typically a model wrapper).