Fix parsing of abstract Unix socket addresses

[viccie30]

These start with a null byte, don't end with a null byte and can contain embedded null bytes.

I changed the type of pathname alternative to OSString, because paths are not necessarily valid UTF-8.

[codecov]

Codecov Report

Attention: Patch coverage is 97.95918% with 1 line in your changes missing coverage. Please review.

Project coverage is 42.12%. Comparing base (f5f4ad7) to head (44c9d11).

Files with missing lines	Patch %	Lines
src/unix/response.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #19      +/-   ##
==========================================
+ Coverage   39.34%   42.12%   +2.77%     
==========================================
  Files          11       11              
  Lines         854      895      +41     
==========================================
+ Hits          336      377      +41     
  Misses        518      518              

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