Refactor batching mechanism, solve threading issue

[lantiga]

Solves with #323 for good, avoiding any shallow copying in the processing thread

[codecov]

Codecov Report

Merging #325 into master will decrease coverage by 0.21%.
The diff coverage is 83.48%.

@@            Coverage Diff             @@
##           master     #325      +/-   ##
==========================================
- Coverage   56.96%   56.75%   -0.22%     
==========================================
  Files          27       27              
  Lines        5080     5050      -30     
==========================================
- Hits         2894     2866      -28     
+ Misses       2186     2184       -2     

Impacted Files	Coverage Δ
src/err.c	91.66% <0.00%> (ø)
src/redisai.h	0.00% <ø> (ø)
src/script.c	60.18% <33.33%> (ø)
src/backends/tflite.c	70.27% <43.75%> (ø)
src/model.c	68.04% <63.82%> (-1.75%)	⬇️
src/backends/onnxruntime.c	68.43% <66.66%> (ø)
src/backends/tensorflow.c	70.68% <72.22%> (ø)
src/backends/torch.c	85.33% <73.33%> (ø)
src/util/queue.c	83.01% <83.01%> (ø)
src/redisai.c	77.13% <86.45%> (-0.18%)	⬇️
... and 5 more

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