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Part of #8130, closes #8719. ## Problem Currently, vectored blob io only coalesce blocks if they are immediately adjacent to each other. When we switch to Direct IO, we need a way to coalesce blobs that are within the dio-aligned boundary but has gap between them. ## Summary of changes - Introduces a `VectoredReadCoalesceMode` for `VectoredReadPlanner` and `StreamingVectoredReadPlanner` which has two modes: - `AdjacentOnly` (current implementation) - `Chunked(<alignment requirement>)` - New `ChunkedVectorBuilder` that considers batching `dio-align`-sized read, the start and end of the vectored read will respect `stx_dio_offset_align` / `stx_dio_mem_align` (`vectored_read.start` and `vectored_read.blobs_at.first().start_offset` will be two different value). - Since we break the assumption that blobs within single `VectoredRead` are next to each other (implicit end offset), we start to store blob end offsets in the `VectoredRead`. - Adapted existing tests to run in both `VectoredReadCoalesceMode`. - The io alignment can also be live configured at runtime. Signed-off-by: Yuchen Liang <yuchen@neon.tech>