zlib: restart format detection when resetting Unzip

[marcopiraccini]

createUnzip().reset() left format detection state from the previous input. After a partial gzip header, the saved header-byte count was not cleared. After detecting gzip or zlib-wrapped deflate, the stream no longer used UNZIP
mode to detect the next input's format.

PR #64620 proposed a similar fix and was closed without merging. This patch tracks whether the stream was created as UNZIP and separates public reset from the internal gzip-member reset. It also tests resetting from detected gzip to deflate.

Fixes: #64619

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.35%. Comparing base (75e4bbe) to head (c1557aa).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66169      +/-   ##
==========================================
- Coverage   90.36%   90.35%   -0.02%     
==========================================
  Files         792      792              
  Lines      275398   275409      +11     
  Branches    52776    52774       -2     
==========================================
- Hits       248877   248844      -33     
- Misses      16937    16988      +51     
+ Partials     9584     9577       -7     

Files with missing lines	Coverage Δ
src/node_zlib.cc	80.37% <100.00%> (+0.16%)	⬆️

... and 31 files with indirect coverage changes

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