feat: add target options with custom mode

[DCjanus]

Close #786

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[darth-raijin]

Would it improve the test quality to structure the assertions as a small table test?

Right now each file/path/assertion is written out separately, but the test follows a pattern:

• Three inputs (file, directory, bytes)
• Each input ends up at a known path inside the container
• Each path has an expected mode that we assert with stat

Representing these as a tiny table (e.g. struct { path, expected_mode } and iterating) would:

• Reduce repetition
• Keep the expected paths and modes in one place
• Make the test easier to extend or refactor in the future.