Add Multi-Emitter

[Lookatator]

Add a base Multi-Emitter implementation of a batch of Emitters.

TODOs:

• [ ] Tests
• [ ] Documentation

[codecov-commenter]

Codecov Report

Merging #90 (1db8b2f) into develop (46e82b6) will increase coverage by 0.07%. The diff coverage is 93.75%.

@@             Coverage Diff             @@
##           develop      #90      +/-   ##
===========================================
+ Coverage    90.69%   90.77%   +0.07%     
===========================================
  Files           84       86       +2     
  Lines         4677     4789     +112     
===========================================
+ Hits          4242     4347     +105     
- Misses         435      442       +7     

Impacted Files	Coverage Δ
qdax/core/emitters/cma_mega_emitter.py	98.63% <66.66%> (-1.37%)	:arrow_down:
qdax/core/emitters/omg_mega_emitter.py	97.95% <66.66%> (-2.05%)	:arrow_down:
qdax/core/emitters/pga_me_emitter.py	99.28% <66.66%> (-0.72%)	:arrow_down:
qdax/core/emitters/emitter.py	90.90% <75.00%> (-3.54%)	:arrow_down:
qdax/core/emitters/multi_emitter.py	96.55% <96.55%> (ø)
...ests/core_test/emitters_test/multi_emitter_test.py	97.36% <97.36%> (ø)
qdax/core/emitters/standard_emitters.py	96.96% <100.00%> (+0.30%)	:arrow_up:

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[Lookatator]

* is it possible to make the lambda function of the update_state a bit less verbose?

Yup! Just did it in the last commit!

* what do you think about computing the start/end indexes only once in the **init** function and storing them as attributes of the class; and use them in state_update. Instead of recomputing them every time. Would potentially improve clarity. What do you think?

I am unsure if they are recomputed everytime (due to the jit...) But indeed, it definitely improves clarity. I just pushed the changes :)

Other then that, I am okay with the batch_size property, I think it is important now that we are starting to work with meta-emitters.

Sounds good! Thanks for the feedback!