[TF] Change eager mode

[felixdittrich92]

This PR:

• move eager mode to the only required part -> exporting to onnx
• boosts inference + training by ~10%

Any feedback is welcome 🤗

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.58%. Comparing base (d0eff67) to head (a4dfdff).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1763      +/-   ##
==========================================
+ Coverage   96.55%   96.58%   +0.02%     
==========================================
  Files         164      164              
  Lines        7895     7895              
==========================================
+ Hits         7623     7625       +2     
+ Misses        272      270       -2     

Flag	Coverage Δ
unittests	96.58% <100.00%> (+0.02%)	⬆️

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