vector-store: create an in memory diskann provider

[Akvear]

In this PR a DiskANNIndex is created in a in-memory DefaultProvider mode using the parameters mapped from VsIndexConfiguration

Fixes: VECTOR-717

[Copilot]

Pull request overview

This PR introduces an initial in-memory DiskANN-backed index factory for vector-store, enabling basic (blocking) vector insert/delete operations and plumbing it into configuration and runtime engine selection.

Changes:

• Add a new DiskANN index implementation (vs_index::diskann) and expose a new_index_factory_diskann constructor.
• Add DiskannAlpha configuration + env var (VECTOR_STORE_DISKANN_ALPHA) and use it to select DiskANN at runtime.
• Add a DiskANN integration test for the /info endpoint and wire DiskANN deps into the workspace.

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
README.md	Documents the new VECTOR_STORE_DISKANN_ALPHA environment variable and cleans up command snippets formatting.
crates/vector-store/tests/integration/info.rs	Adds an integration test asserting DiskANN engine version is reported by /info.
crates/vector-store/src/vs_index/mod.rs	Exposes the new diskann index module.
crates/vector-store/src/vs_index/diskann.rs	Implements an in-memory DiskANN provider + actor handling Add/Remove (search/count currently unimplemented).
crates/vector-store/src/main.rs	Selects DiskANN factory when diskann_alpha is set in config.
crates/vector-store/src/lib.rs	Adds DiskannAlpha, adds it to Config, and exposes new_index_factory_diskann.
crates/vector-store/src/config_manager.rs	Parses VECTOR_STORE_DISKANN_ALPHA into config and adds a config loading test.
crates/vector-store/Cargo.toml	Adds DiskANN crates to the vector-store crate deps.
Cargo.toml	Adds git-based workspace deps for DiskANN crates.
Cargo.lock	Locks DiskANN and its transitive dependencies.

[Copilot]

Pull request overview

Copilot reviewed 9 out of 10 changed files in this pull request and generated 4 comments.

Comments suppressed due to low confidence (1)

crates/vector-store/src/vs_index/diskann.rs:193

• primary_id_to_u32 performs a lossy u64 -> u32 cast. This can cause ID collisions (and incorrect deletes/search results) whenever PrimaryId exceeds u32::MAX or when epochs differ, leading to silent index corruption.

// TODO: DiskANN's provider hardcodes `ExternalId = u32`, while vector-store keys are
// `u64` [`PrimaryId`]s (a 16-bit epoch packed with a row index). For this PoC we
// simply cast the `PrimaryId` down to `u32`, which silently truncates the upper bits
// (including the epoch) and can make distinct primary ids collide. Replace with a proper
// dense `u32 <-> PrimaryId` mapping before this is used beyond a baseline.
fn primary_id_to_u32(primary_id: PrimaryId) -> u32 {
    u64::from(primary_id) as u32
}

[Akvear]

Changes:

• Changed the order of the last 2 commits
• Removed test imports already in production
• Removed test helper, since it's only used in 1 place
• Removed unused TryFrom impl

[Akvear]

Changes:

• joined the 2 troublesome commits
• added explanation to why crates are neede

[Akvear]

Changes:

• moved the index into the async block in the new() function