irmin-pack-tools: Add base58 support for ppidx

[clecat]

Adds the dump of the hashes in base58 alongside the base64 as asked by @art-w

[codecov-commenter]

Codecov Report

Merging #2266 (a6d07c5) into main (514e7ba) will decrease coverage by 0.01%.
Report is 3 commits behind head on main.
The diff coverage is 92.00%.

❗ Current head a6d07c5 differs from pull request most recent head 9b7ad61. Consider uploading reports for the commit 9b7ad61 to get more accurate results

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@@            Coverage Diff             @@
##             main    #2266      +/-   ##
==========================================
- Coverage   68.20%   68.19%   -0.01%     
==========================================
  Files         138      138              
  Lines       16739    16739              
==========================================
- Hits        11416    11415       -1     
- Misses       5323     5324       +1     

Files Changed	Coverage Δ
src/irmin-pack/inode.ml	79.43% <90.47%> (ø)
src/irmin-pack/pack_value.ml	86.81% <100.00%> (ø)

... and 1 file with indirect coverage changes

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[metanivek]

LGTM! I'm happy with the simplified solution!