[timeseries] add some basic block and deepAR model

[Carkham]

trafficstars

Description

This PR adds two new sections for creating trainable models.

The first part is embedding and scaler, which are responsible for encoding the input features and scaling the target values.

The second part is that we implemented a deepAR network model with the above-mentioned blcok, which refers to the implementation in gluonTS.

Since the model predicts a probability distribution, we need to override the different forward methods when training and inference with different block.

[codecov-commenter]

Codecov Report

Base: 72.08% // Head: 71.36% // Decreases project coverage by -0.72% :warning:

Coverage data is based on head (644150a) compared to base (bb5073f). Patch coverage: 71.66% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2027      +/-   ##
============================================
- Coverage     72.08%   71.36%   -0.73%     
- Complexity     5126     6275    +1149     
============================================
  Files           473      624     +151     
  Lines         21970    27795    +5825     
  Branches       2351     2997     +646     
============================================
+ Hits          15838    19835    +3997     
- Misses         4925     6500    +1575     
- Partials       1207     1460     +253     

Impacted Files	Coverage Δ
api/src/main/java/ai/djl/modality/cv/Image.java	69.23% <ø> (-4.11%)	:arrow_down:
...rc/main/java/ai/djl/modality/cv/MultiBoxPrior.java	76.00% <ø> (ø)
...rc/main/java/ai/djl/modality/cv/output/Joints.java	71.42% <ø> (ø)
.../main/java/ai/djl/modality/cv/output/Landmark.java	100.00% <ø> (ø)
...main/java/ai/djl/modality/cv/output/Rectangle.java	72.41% <0.00%> (ø)
...i/djl/modality/cv/translator/BigGANTranslator.java	21.42% <0.00%> (-5.24%)	:arrow_down:
.../modality/cv/translator/ImageFeatureExtractor.java	0.00% <0.00%> (ø)
.../ai/djl/modality/cv/translator/YoloTranslator.java	27.77% <0.00%> (+18.95%)	:arrow_up:
...modality/cv/translator/wrapper/FileTranslator.java	44.44% <ø> (ø)
...y/cv/translator/wrapper/InputStreamTranslator.java	44.44% <ø> (ø)
... and 563 more

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