v0.4.0-alpha.2

What's Changed

• refactor: rework quantization abstraction by @usamoi in #591
• feat: add metrics dot and cos by @cutecutecat in #566
• refactor: rabitq by @usamoi in #593
• docs: delete sparse vector search comparison in readme by @JinweiOS in #595
• refactor: use transposed centroids in PQ preprocess by @usamoi in #594
• fix: reduce length of directory name by @usamoi in #588

Full Changelog: v0.4.0-alpha.1...v0.4.0-alpha.2