fstree: add compressed object decompression tool

[End-rey]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 62.93436% with 96 lines in your changes missing coverage. Please review.
✅ Project coverage is 26.82%. Comparing base (6180c09) to head (0c03868).
⚠️ Report is 19 commits behind head on master.

Files with missing lines	Patch %	Lines
...ject_storage/blobstor/fstree/rewrite_compressed.go	57.94%	26 Missing and 19 partials ⚠️
...torage/blobstor/fstree/rewrite_compressed_linux.go	52.17%	17 Missing and 16 partials ⚠️
cmd/fstree-decompress/root.go	78.31%	10 Missing and 8 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4079      +/-   ##
==========================================
+ Coverage   26.28%   26.82%   +0.53%     
==========================================
  Files         671      675       +4     
  Lines       45862    45941      +79     
==========================================
+ Hits        12056    12322     +266     
+ Misses      32674    32453     -221     
- Partials     1132     1166      +34     

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[carpawell]

if it is an FSTree method, why do we need this utility then? it can be a background routing for the next release

[roman-khimov]

Theoretically, yes, I also had this thought, but:

• either it needs to be synchronized with other activities (deletion first of all to avoid object resurrection) which requires some effort
• or it keeps the same logic as an outsider, but then having a separate process is easier, can be controlled by shard and can even be performed before the release