Bump version to 0.56.0

[Copilot]

Version bump 0.55.0 → 0.56.0 to cover two merged PRs since the last release.

Breaking changes

PQ computers: Deref generic replaced with lifetime (#1247)

DistanceComputer and QueryComputer in pq::distance now borrow the table via a lifetime instead of owning/dereffing it:

// Before
type DistanceComputer = pq::distance::DistanceComputer<Arc<FixedChunkPQTable>>;

// After
type DistanceComputer<'a> = pq::distance::DistanceComputer<'a>;
// construction: pass &self.pq_chunk_table instead of .clone()

Update type aliases, associated-type bounds, and construction sites accordingly.

Non-breaking

• diskann-garnet persistence (#1251): Q8 start-point cache and BIN codebook + backfill flag are now saved and reloaded; index resumes in quantized mode after restart.

Checklist

• workspace.package.version and all [workspace.dependencies] versions updated
• CHANGELOG entry added
• CI and dry-run publish check pass