fast forward seeks on compressed streams

[oh6hay]

The compressed_stream_io.py discarded the uncompressor on forward seeks, making it really slow to access the stream if the use pattern consisted of a large number of (small) forward seeks. I found this bug by investigating why log2timeline/plaso failed on a stuck worker that attempted to analyze a fairly large xz compressed tarball -- enumerating the tar contents thrashed the CompressedStream because it initialized a new decompressor and decompressed the entire stream on every forward seek.

The fix makes the CompressedStream retain the decompressor and when initialized, only discard it when seeking backwards, as compressed streams generally cannot be seeked backwards. Prior to the fix, small forward seeks caused the decompressor be initialized and decompress the entire stream up to the new seek position.

I included a test case that checks that 5000 forward seeks on a large xz-compressed stream of random bytes happens reasonably fast. (The compressed data shouldn't be a repeated pattern as that compresses too well, causing the test not to fail on an unfixed CompressedStream implementation)

[codecov]

Codecov Report

❌ Patch coverage is 90.47619% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.86%. Comparing base (0f55fbc) to head (28c24a2).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
dfvfs/file_io/compressed_stream_io.py	90.47%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #807      +/-   ##
==========================================
+ Coverage   87.84%   87.86%   +0.01%     
==========================================
  Files         297      297              
  Lines       12287    12296       +9     
==========================================
+ Hits        10794    10804      +10     
+ Misses       1493     1492       -1     

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