fix: fix boolean inline constant decoding

[Xuanwo]

This fixes a regression where reading a dataset could fail with:

Inline constant is not supported for non-fixed-stride data type Boolean

---

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

P0 Issue: Silent data corruption risk with debug_assert

Location: rust/lance-arrow/src/scalar.rs:143-168

The PR removes runtime validation and replaces it with debug_assert checks. This is dangerous because:

1. debug_assert is compiled out in release builds - In release mode, if the inline value length doesn't match expectations (e.g., due to data corruption, format changes, or bugs in upstream code), the code will silently proceed with incorrect data instead of failing fast.

2. The original error handling served as a safety net - The original code returned proper errors when invariants were violated, which would surface bugs early and prevent silent data corruption.

Recommendation: Keep the original runtime validation. While the PR description says this is "per maintainer preference", the trade-off here favors safety. At minimum, the length check should remain as a runtime error:

// Keep runtime validation for boolean
if matches\!(data_type, DataType::Boolean) {
    if inline_value.len() \!= 1 {
        return Err(ArrowError::InvalidArgumentError(format\!(
            "Invalid boolean inline scalar length (expected 1 byte, got {})",
            inline_value.len()
        )));
    }
} else {
    let byte_width = data_type.byte_width_opt().ok_or_else(|| {
        ArrowError::InvalidArgumentError(format\!(
            "Inline constant is not supported for non-fixed-stride data type {:?}",
            data_type
        ))
    })?;
    
    if inline_value.len() \!= byte_width {
        return Err(ArrowError::InvalidArgumentError(format\!(
            "Inline constant length mismatch for {:?}: expected {} bytes but got {}",
            data_type, byte_width, inline_value.len()
        )));
    }
}

P1 Issue: Missing test for false boolean value

The unit test only covers true. Add a test for false to ensure the bit-packing is handled correctly for both values:

#[test]
fn test_inline_value_boolean_false_round_trip() {
    let scalar: ArrayRef = Arc::new(BooleanArray::from_iter([Some(false)]));
    let inline = try_inline_value(&scalar).unwrap();
    let decoded = decode_scalar_from_inline_value(&DataType::Boolean, &inline).unwrap();
    assert_eq\!(decoded.len(), 1);
    assert\!(\!decoded.as_boolean().value(0));
}

---

The fix for the boolean inline constant decoding regression is correct in principle. The tests are well-structured. The main concern is the removal of runtime validation.

[Xuanwo]

Test failed for:

dataset::scanner::test::test_ann_prefilter::data_storage_version_2_LanceFileVersion__Stable::stable_row_ids_1_false::index_params_2_VectorIndexParams__with_ivf_hnsw_sq_params_MetricType__L2_IvfBui stdout ----

thread 'dataset::scanner::test::test_ann_prefilter::data_storage_version_2_LanceFileVersion__Stable::stable_row_ids_1_false::index_params_2_VectorIndexParams__with_ivf_hnsw_sq_params_MetricType__L2_IvfBui' (18589) panicked at rust/lance/src/dataset/scanner.rs:5839:9:
assertion `left == right` failed
  left: 6
 right: 11

It's another flaky test and not related to my changes,