Add a lazy-loading mechanic

[PythonFZ]

If you have nested Node structures you don't want to load everything but only the files you really need. With lazy the file will only be read when accessed via __get__ and therefore the memory will not be filled with unneccessary data.

Explanation of changes can best be found at https://github.com/zincware/ZnTrack/blob/add_lazy/examples/docs/09_lazy.ipynb

TODOs

• Add documentation
• check that config.lazy does anything
• fix notebooks

[codecov]

Codecov Report

Merging #236 (29f8446) into main (d8b9eff) will decrease coverage by 0.81%.
The diff coverage is 61.22%.

@@            Coverage Diff             @@
##             main     #236      +/-   ##
==========================================
- Coverage   69.44%   68.62%   -0.82%     
==========================================
  Files          23       23              
  Lines         985     1023      +38     
  Branches      183      195      +12     
==========================================
+ Hits          684      702      +18     
- Misses        284      298      +14     
- Partials       17       23       +6     

Flag	Coverage Δ
unittests	68.62% <61.22%> (-0.82%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
zntrack/utils/utils.py	70.10% <0.00%> (ø)
zntrack/core/dvcgraph.py	67.14% <33.33%> (-1.75%)	⬇️
zntrack/core/base.py	82.43% <50.00%> (-5.81%)	⬇️
zntrack/utils/__init__.py	85.71% <66.66%> (-14.29%)	⬇️
zntrack/core/zntrackoption.py	83.33% <72.72%> (-5.31%)	⬇️
zntrack/dvc/__init__.py	98.33% <100.00%> (ø)
zntrack/utils/config.py	100.00% <100.00%> (ø)
zntrack/descriptor/__init__.py	85.71% <0.00%> (-11.43%)	⬇️

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[SamTov]

Looks like a really nice addition. I looked over the notebooks and maybe some more comments to it for additional support. On an unrelated topic, is there much one can do about the excess stdout from DVC?