feat: add blob handling support for fragment

[Xuanwo]

This PR will add blob handling support for fragment

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Parts of this PR were drafted with assistance from Codex (with gpt-5.2) and fully reviewed and edited by me. I take full responsibility for all changes.

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Code Review

Overall: This PR correctly adds blob handling support to fragment scanning, mirroring the existing Dataset scanner implementation. The changes are well-structured and consistent with the codebase patterns.

Minor Suggestion (P2)

The test covers fragment.scanner().to_table() and fragment.to_table(), but fragment.to_batches() also receives the new blob_handling parameter. Consider adding a brief test case for to_batches as well for completeness:

batches = list(fragment.to_batches(columns=["blobs"], blob_handling="all_binary"))
assert pa.Table.from_batches(batches).column("blobs").to_pylist() == values

This is a minor suggestion - the current coverage is likely sufficient since to_batches simply delegates to scanner().

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LGTM otherwise. The implementation correctly follows the existing pattern in dataset.rs.