[BREAKING] Drop TensorFlow backend

[felixT2K]

This PR:

• Remove all TensorFlow content
• Add PyTorch as fixed dependency
• Drop documentation versions which rely on TensorFlow backend
• Remove conda which does not support PyTorch builds anymore - since 2.15

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.27%. Comparing base (d01acdd) to head (d297a9c). Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1967      +/-   ##
==========================================
- Coverage   96.93%   96.27%   -0.66%     
==========================================
  Files         172      141      -31     
  Lines        8633     6037    -2596     
==========================================
- Hits         8368     5812    -2556     
+ Misses        265      225      -40     

Flag	Coverage Δ
unittests	96.27% <100.00%> (-0.66%)	:arrow_down:

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[felixdittrich92]

NOTE: API test will fail until merged

[felixdittrich92]

@sebastianMindee That should be everything for a first round to get rid of TensorFlow :sweat: :sweat_smile: API test should be green after it's merged