[WIP] Add kernel decision tree - Gaussian, Gabor, etc.

[adam2392]

Fixes #20

Changes proposed in this pull request:

• implements a base class for kernel defined decision trees
• Implements n-dim Gaussian Kernel
• implement n-dim Wavelet Kernel
• Implements 2D Gabor kernel

To build 1D filter bank of wavelets: https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.morlet.html#scipy.signal.morlet

To build 2D filter bank of Gabor kernel:
https://scikit-image.org/docs/stable/api/skimage.filters.html#gabor-kernel

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[codecov]

Codecov Report

Patch coverage: 17.64% and project coverage change: -3.26 ⚠️

Comparison is base (32162e4) 92.64% compared to head (33e9875) 89.39%.

❗ Current head 33e9875 differs from pull request most recent head ca00632. Consider uploading reports for the commit ca00632 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #70      +/-   ##
==========================================
- Coverage   92.64%   89.39%   -3.26%     
==========================================
  Files          12       10       -2     
  Lines        1142      924     -218     
==========================================
- Hits         1058      826     -232     
- Misses         84       98      +14     

Impacted Files	Coverage Δ
sktree/tree/_classes.py	78.80% <17.64%> (-8.16%)	⬇️

... and 9 files with indirect coverage changes

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