Bnb/sup3r mini model

[bnb32]

Added recursive layer initialization in HiddenLayers and Sup3rObsModel which can be built from nested hidden layers in a config, and also ingest multiple obs features / exo features.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 85.45455% with 24 lines in your changes missing coverage. Please review.

Project coverage is 88.43%. Comparing base (1ba45b2) to head (541012c). Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
phygnn/layers/custom_layers.py	65.90%	15 Missing :warning:
phygnn/utilities/tf_utilities.py	85.45%	8 Missing :warning:
tests/test_tf_utilities.py	98.03%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #64      +/-   ##
==========================================
+ Coverage   87.89%   88.43%   +0.53%     
==========================================
  Files          27       27              
  Lines        3577     3708     +131     
==========================================
+ Hits         3144     3279     +135     
+ Misses        433      429       -4     

Flag	Coverage Δ
unittests	88.43% <85.45%> (+0.53%)	:arrow_up:

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