chunker permutation

[ncleaton]

Make the buzhash chunker more resistant to fingerprinting by introducing a permutation of the buzhash table, as discussed at #3687

[codecov-io]

Codecov Report

Merging #4921 into master will increase coverage by 0.01%.
The diff coverage is 92.3%.

@@            Coverage Diff             @@
##           master    #4921      +/-   ##
==========================================
+ Coverage   83.73%   83.75%   +0.01%     
==========================================
  Files          37       37              
  Lines        9776     9798      +22     
  Branches     1623     1627       +4     
==========================================
+ Hits         8186     8206      +20     
- Misses       1112     1113       +1     
- Partials      478      479       +1

Impacted Files	Coverage Δ
src/borg/archive.py	82.52% <100%> (+0.13%)	⬆️
src/borg/crypto/key.py	86.68% <91.3%> (+0.16%)	⬆️
src/borg/archiver.py	81.17% <0%> (-0.11%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update fc96fc4...a4b3081. Read the comment docs.

[ThomasWaldmann]

i am currently rather busy otherwise, so reviewing this might still take a while...

[ThomasWaldmann]

hi @ncleaton!

could you please re-do this PR from a non-master branch?

i'ld like to work on it, but it does not let me push to your master...

[ncleaton]

replaced by #5070