Remove channel concept (python side)

[lferran]

Description

We’re not using it.
It doubles the number of integration tests we have.
Will speed up our CI

How was this PR tested?

Describe how you tested this PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.26%. Comparing base (31ce460) to head (cc302a7).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2454      +/-   ##
==========================================
+ Coverage   86.20%   86.26%   +0.05%     
==========================================
  Files         373      373              
  Lines       23119    23102      -17     
==========================================
- Hits        19929    19928       -1     
+ Misses       3190     3174      -16     

Flag	Coverage Δ
nucliadb	73.79% <100.00%> (+0.05%)	⬆️
nucliadb-ingest	29.29% <100.00%> (-0.03%)	⬇️
nucliadb-reader	25.18% <100.00%> (-0.03%)	⬇️
nucliadb-search	36.94% <100.00%> (-0.02%)	⬇️
nucliadb-standalone	47.32% <100.00%> (-0.03%)	⬇️
nucliadb-train	45.95% <100.00%> (-0.03%)	⬇️
nucliadb-writer	40.27% <100.00%> (-0.03%)	⬇️
nucliadb_dataset	55.31% <ø> (ø)
nucliadb_models	85.14% <ø> (+0.04%)	⬆️
nucliadb_sdk	78.26% <ø> (ø)
nucliadb_sidecar	89.03% <ø> (ø)
nucliadb_telemetry	86.55% <ø> (ø)
nucliadb_utils	84.06% <ø> (-0.01%)	⬇️

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