fix: s3: isdir()

[namachan10777]

Fix a bug in S3 where it incorrectly identified simple prefix matches as directories.

When a partially matching key already exists as shown below, and MaxKeys=1 is set to 1, bus/ would be retrieved first, but since it's not bush, the operation would fail, resulting in the directory being incorrectly identified as non-existent.

• bus/engine.txt
• bush/kusamura.txt

The solution is to prepend a / suffix when performing the List operation and determine existence based on whether a Common Prefix or Contents exist. If at least one exists, we can safely consider this prefix as a directory presence, and the presence of the / suffix prevents simple prefix matching from failing.

Related Issue(PR)s

closes #379

Effect

This is a just bug fix.

[Copilot]

Pull request overview

This PR fixes pfio.v2.S3.isdir() incorrectly treating forward-prefix collisions (e.g., abc vs abcde) as “non-existent directory” when list_objects_v2(MaxKeys=1) returns a non-matching prefix first. The fix makes the S3 listing unambiguous by querying with a trailing slash and considers the directory present if S3 returns either Contents or CommonPrefixes.

Changes:

• Update S3.isdir() to use Prefix=f"{key}/" and determine existence via presence of Contents/CommonPrefixes.
• Add a regression test that exercises prefix-collision cases (abc/ vs abcde/, and nested xyz/abc*).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
pfio/v2/s3.py	Adjusts isdir() S3 listing logic to avoid forward-prefix collisions and correctly detect directory presence.
tests/v2_tests/test_s3.py	Adds coverage for the prefix-collision regression scenario.

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