Remove redundant BufReaders for decompressing tar archives

[kskalski]

Problem

ZSTD Decoder::new creates buf reader with tuned size already, other decoders handle buffering too:

• BzDecoder https://docs.rs/bzip2/latest/src/bzip2/read.rs.html#87-91
• GzDecoder https://docs.rs/flate2/latest/src/flate2/gz/read.rs.html#143-147
• lz4::Decoder https://docs.rs/lz4/1.28.1/src/lz4/decoder.rs.html#33-43 (it uses a vec buffer directly)
• zstd::Decoder https://github.com/gyscos/zstd-rs/blob/229054099aa73f7e861762f687d7e07cac1d9b3b/src/stream/read/mod.rs#L29

In those cases wrapping reader with BufReader is counter-productive or unnecessary (bzip2 provides both bufread and read decoders)

Summary of Changes

Remove redundant BufReaders for decompressing tar archives when underlying decompressor is already doing buffering.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 82.8%. Comparing base (103fb21) to head (71e2436).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##           master    #6317     +/-   ##
=========================================
- Coverage    82.8%    82.8%   -0.1%     
=========================================
  Files         847      847             
  Lines      379488   379486      -2     
=========================================
- Hits       314349   314309     -40     
- Misses      65139    65177     +38     

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[brooksprumo]

ZSTD Decoder::new creates buf reader with tuned size already (https://github.com/gyscos/zstd-rs/blob/229054099aa73f7e861762f687d7e07cac1d9b3b/src/stream/read/mod.rs#L29), most others have some form of buffering too, so wrapping reader with BufReader is counter-productive.

Thanks for the link to where zstd creates its own BufReader. Can you also provide links for gzip and lz4 too, since this PR is changing them as well.

[kskalski]

Sure, I'm also switching bzip2 decoder as it has appropriate wrapper. Updated description.

[brooksprumo]

Looks good to me. I think you'll need to rebase to pull in newer commits that fix the CI.

[brooksprumo]

[brooksprumo]

Let's also backport this to v2.3. We'll need to wait for #6430 to land, and then please add the "v2.3" label to kickoff the backport.