Switch from libflate to flate2

[mkrasnitski]

The flate2 crate is more popular and as far as I can tell, inferno makes no attempt to be no_std. The GzDecoder::new constructor is infallible because libflate attempts to read and validate the gzip header on construction, whereas flate2 does not and waits until the decoder is actually used to perform validation. Additionally, flate2 uses a BufReader internally, though GzDecoder only exposes a Read interface.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.22%. Comparing base (51423f4) to head (ea02b40).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #361   +/-   ##
=======================================
  Coverage   91.22%   91.22%           
=======================================
  Files          21       21           
  Lines        4272     4272           
=======================================
  Hits         3897     3897           
  Misses        375      375           

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