feat(parquet): RowSelection can be backed by a BooleanBuffer

[haohuaijin]

Which issue does this PR close?

• Closes Allow RowSelection to be backed by a BooleanBuffer #10140

Rationale for this change

RowSelection currently stores selections as Vec<RowSelector> (16 bytes per selector). This is compact for long runs, but expensive for scattered matches. With ~35% isolated single-row hits, it uses about 11.2 bytes per input row. A BooleanBuffer uses 1 bit per input row, about 90x less memory.

The reader can also choose the Mask strategy, which converts selectors back into a bitmap. When the caller already had a bitmap, this conversion round-trip is unnecessary.

What changes are included in this PR?

RowSelection can now be backed by either Vec<RowSelector> or BooleanBuffer. New public construction:

pub fn RowSelection::from_boolean_buffer(mask: BooleanBuffer) -> Self;
impl From<BooleanBuffer> for RowSelection;

Methods that can work directly on the bitmap now do so:

• iter() streams via BitSliceIterator
• row_count / skipped_row_count use count_set_bits
• selects_any uses set_indices().next()
• trim preserves mask backing via BooleanBuffer::slice
• intersection / union on Mask+Mask use BitAnd / BitOr
• split_off on a mask uses BooleanBuffer::slice (O(1), both halves stay mask-backed)
• limit slices at the selected-row boundary via find_nth_set_bit_position, staying mask-backed
• offset finds the first selected row to keep via find_nth_set_bit_position and rebuilds only the mask buffer, avoiding selector materialization
• and_then applies the inner selection over the mask's set positions, returning a mask-backed result
• FromIterator<RowSelection> concatenates BooleanBuffers when every input is mask-backed

Mixed inputs, and existing selector-backed inputs, still use the existing selector helpers. Existing callers keep the same behavior.

The reader (ReadPlanBuilder::build) passes a mask-backed selection straight to RowSelectionCursor::new_mask_from_buffer, so it skips rebuilding the bitmap from selectors.

Are these changes tested?

Yes. This PR extends the existing RowSelection unit tests with coverage for:

• constructing from BooleanBuffer, including empty and all-unset masks
• From<BooleanBuffer>
• preserving mask backing across clone, split_off, limit, offset, and_then, and all-mask FromIterator<RowSelection>
• falling back to selector backing for mixed-backed concatenation
• equality between equivalent selector-backed and mask-backed selections
• mask-backed intersection / union, including uneven-length inputs
• fuzz-style equivalence between mask-backed selections and the existing from_filters selector path

Are there any user-facing changes?

Yes — one source-breaking change suitable for the next major release: RowSelection::iter() now yields RowSelector (Item = RowSelector) instead of &RowSelector. This is needed because a mask-backed selection does not have a Vec<RowSelector> to borrow from.

RowSelector is Copy (16 bytes), so most call sites are source-compatible:

selection.iter().map(|s| s.row_count).sum::<usize>()    // unchanged
selection.iter().filter(|s| !s.skip).count()            // unchanged
selection.iter().any(|s| !s.skip)                       // unchanged

Call sites that need updating:

// before
let v: Vec<RowSelector> = selection.iter().cloned().collect();
let v: Vec<&RowSelector> = selection.iter().collect();

// after
let v: Vec<RowSelector> = selection.iter().collect();

Within arrow-rs, the required updates are limited to parquet's own RowSelection code and tests. The other crates do not use RowSelection::iter().