Add testing with inferred data

[ablaom]

Define test(model; options...) to test a single model and infer the datasets to use.

Dump model-type-specific tests, such as test_single_target_classifiers.

[codecov]

Codecov Report

Attention: 23 lines in your changes are missing coverage. Please review.

Comparison is base (6ccbae4) 82.42% compared to head (96efa86) 87.84%.

Files	Patch %	Lines
src/test.jl	4.34%	22 Missing ⚠️
src/datasets.jl	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev      #38      +/-   ##
==========================================
+ Coverage   82.42%   87.84%   +5.42%     
==========================================
  Files           5        5              
  Lines         256      255       -1     
==========================================
+ Hits          211      224      +13     
+ Misses         45       31      -14     

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