Add prediction type check for Explicit strategy

[ablaom]

Closes #200

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e3293dc) 86.44% compared to head (961faee) 87.17%.
Report is 3 commits behind head on dev.

❗ Current head 961faee differs from pull request most recent head 53700b3. Consider uploading reports for the commit 53700b3 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #201      +/-   ##
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+ Coverage   86.44%   87.17%   +0.73%     
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  Files          13       13              
  Lines         649      655       +6     
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+ Hits          561      571      +10     
+ Misses         88       84       -4     

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[OkonSamuel]

Looks good.
Just a small note, this actually depends on the measure used. What if the user defined a measure that supports both probabilistic and deterministic predictions (That's possible). So it would be possible to use models with different prediction types.
Personally, I would have gone for a forced warning, that tells the user to make that the measure they are using could support that. But maybe that may also have it downsides.

[ablaom]

(That's possible)

Good point, I hadn't thought of that. As it turns out it's not possible, but only because of bug. So I'm waiting on:

• Fix Resampler update bug MLJBase.jl#954

and then I'll update this PR.