Magic test for archives with zero-length entry

[noahp]

Noticed when attempting to unpack a python .whl wheel file;
They're just renamed .zip's, and usually work OK, but there are casess
where the first file in the .whl archive is zero bytes, and that
causes file -z to error:

❯ file -zL tests/test-1.23.zip
tests/test-1.23.zip: ERROR:[gzip: ] (data)

❯ file tests/test-1.23.zip
tests/test-1.23.zip: Zip archive data, made by v2.3 UNIX, extract using at least v1.0, last modified Oct 28 2006 14:38:44, uncompressed size 0, method=store

❯ unzip -l tests/test-1.23.zip
Archive:  tests/test-1.23.zip
  Length      Date    Time    Name
---------  ---------- -----   ----
        0  2006-10-28 14:38   1/2/3
        0  2006-10-28 14:38   a/b
        0  2006-10-28 14:38   foobar
---------                     -------
        0                     3 files

This means we were not using file magic for any archive that started
with a zero-length file (or directory) entry.

Add a fallback when the magic test fails in this case, and add a test to
cover it.

[Copilot]

Pull request overview

This PR fixes a bug where file -z fails to detect archives when the first entry is zero-length, and adds test coverage for this scenario. Python wheel files commonly have zero-byte entries at the beginning, which previously caused magic detection to fail.

Key changes:

• Add fallback logic to retry file command without -z flag when ERROR is detected
• Add test case with a .whl file containing zero-length entries
• Move output reading and processing after error checking

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 1 comment.

File	Description
dtrx/dtrx.py	Adds error detection and fallback logic to retry without -z flag when file command encounters ERROR on zero-length archive entries
tests/tests.yml	Adds test case for .whl files with zero-length entries
tests/test-1.23.whl	Adds test fixture containing a wheel archive with zero-length entries

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