Add simple tree navigation helper

[alexamici]

[codecov-commenter]

Codecov Report

Merging #118 (aeeb481) into main (08b33bc) will decrease coverage by 0.11%. The diff coverage is 91.66%.

@@            Coverage Diff             @@
##             main     #118      +/-   ##
==========================================
- Coverage   96.89%   96.78%   -0.12%     
==========================================
  Files          13       15       +2     
  Lines        1063     1087      +24     
  Branches      132      133       +1     
==========================================
+ Hits         1030     1052      +22     
- Misses         15       16       +1     
- Partials       18       19       +1     

Impacted Files	Coverage Δ
xarray_sentinel/treenav.py	77.77% <77.77%> (ø)
tests/test_40_treenav.py	100.00% <100.00%> (ø)
xarray_sentinel/__init__.py	100.00% <100.00%> (ø)
xarray_sentinel/sentinel1.py	95.31% <100.00%> (+<0.01%)	:arrow_up:

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