Refactored _read_first_bytes to _file_startswith for clarity of use

[Copilot]

• Understand current implementation of _read_first_bytes
• Replace _read_first_bytes with _file_startswith helper function
• Update _content_is_retrieved to use the new function
• Remove the old _read_first_bytes function
• Create tests to validate the new implementation
• Run linting and type checking
• Run existing tests to ensure no regressions
• Request code review and address feedback
• Rename parameter s to string per review feedback
• Final verification and security check

Summary

Successfully refactored _read_first_bytes to _file_startswith as requested in issue #166.

Changes:

• Replaced _read_first_bytes(file_path, n=6) with _file_startswith(file_path, string)
• New function takes a string parameter instead of integer, making the intent clearer
• Eliminates hardcoded value 6 (which was len("/annex"))
• Returns boolean directly instead of bytes for comparison
• Updated call: _read_first_bytes(file_path=file_path, n=6) != b"/annex" → not _file_startswith(file_path=file_path, string="/annex")

Testing:

✅ All custom tests pass (basic and real-world scenarios)
✅ Existing unit tests pass
✅ Linting passes (ruff)
✅ Type checking passes (mypy)
✅ No security issues (CodeQL)

Security Summary:

No security vulnerabilities detected in the changes.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Minor style: refactor _read_first_bytes</issue_title>
<issue_description>FWIW - I think it is a better workflow for us, when dealing with such small suggestions, to split them as separate issues 'to follow-up on' separately from the main PR since they aren't really core to the functionality (in that case, a core bug fix) and shouldn't block such merges

I have no problem with the suggestion below, and will do it in a separate PR

dang, you are right! It is a little surprising though. Anyways, I do not feel it is worth a dedicated function really here, if anything could be _file_startswith(file_path: Path, s: str) to make its purpose of living to do f.read(len(s)) == s thus avoiding here hardcoded value of 6 to match len("/annex"). but whatever -- let's just keep going

Originally posted by @yarikoptic in #165 (comment)
</issue_description>

<agent_instructions>This should be an easy one - replace _read_first_bytes with the direct startswith check</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Minor style: refactor _read_first_bytes #181

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.48%. Comparing base (76689e8) to head (807e1e2).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #287      +/-   ##
==========================================
+ Coverage   84.12%   84.48%   +0.35%     
==========================================
  Files          36       36              
  Lines        1392     1424      +32     
==========================================
+ Hits         1171     1203      +32     
  Misses        221      221              

Flag	Coverage Δ
unittests	84.48% <100.00%> (+0.35%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/nwb2bids/_converters/_datalad_utils.py	100.00% <100.00%> (ø)

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