fix: fix mini-block dictionary bitpacking panic

[Xuanwo]

Fix a panic in mini-block dictionary decode when the dictionary buffer uses bitpacking encodings.

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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.

[github-actions]

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[github-actions]

Code Review

Overall Assessment: This is a well-structured bug fix that addresses a real panic when using mini-block dictionary encoding with bitpacking compression.

Positive Aspects

• The fix correctly handles InlineBitpacking and OutOfLineBitpacking dictionary encodings
• Good refactoring that reduces code duplication in MiniBlockScheduler::try_new
• The change from unreachable!() to Error::InvalidInput for unrecognized encodings improves robustness
• Both unit test and end-to-end integration test are included

P1: Minor Issues

1. Test assertion could be more precise (dataset_scanner.rs:467): The assertion checks that the encoding string contains both "OutOfLineBitpacking" and "dictionary", but the format of describe_encoding() output could change. Consider using a more structured way to verify the encoding if available.

Suggestions (non-blocking)

• The end-to-end test is thorough but could benefit from verifying the actual data values after scanning (currently only checks column count).

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Automated review by Claude

[codecov]

Codecov Report

❌ Patch coverage is 83.67347% with 8 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../lance-encoding/src/encodings/logical/primitive.rs	83.67%	7 Missing and 1 partial ⚠️

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