Implement filter search for disk path using AdpativeL

[dyhyfu]

This PR is to add filter search to disk path using AdpativeL filter algorithm.

Reference PR: #1131

The main changes:

1. New filter_search() method on DiskIndexSearcher (parallel to flat_search) that constructs InlineFilterSearch::new(Knn, label_provider, adaptive_l) and hands it to the same self.index.search(...) engine as the plain Knn path.
2. New PredicateLabelProvider that adapts the existing &dyn Fn(&u32) -> bool to QueryLabelProvider
3. search() and search_internal() gain adaptive_l: Option. When None, behavior is identical to today. When Some(_), the graph path routes through filter_search.
4. Three-way dispatch in search_internal: flat scan → graph + adaptive_l → plain Knn.

[Copilot]

Pull request overview

This PR adds an AdaptiveL-enabled, inline label-filtered graph-search path for disk index search, wiring it through DiskIndexSearcher while keeping existing behavior unchanged when AdaptiveL is not provided.

Changes:

• Add adaptive_l: Option<AdaptiveL> to DiskIndexSearcher::search / search_internal and dispatch to an InlineFilterSearch path when present.
• Introduce a small PredicateLabelProvider adapter to bridge the existing &dyn Fn(&u32) -> bool filter predicate into QueryLabelProvider<u32>.
• Add disk-provider tests covering (1) no-op equivalence vs plain Knn and (2) selective predicates returning only matching IDs; update callers to pass None until CLI/JSON exposes AdaptiveL.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
diskann-tools/src/utils/search_disk_index.rs	Passes None for the new adaptive_l argument (not yet exposed via CLI).
diskann-disk/src/search/provider/disk_provider.rs	Implements filter_search via InlineFilterSearch + AdaptiveL, adds adapter + tests, and extends search APIs with adaptive_l.
diskann-disk/src/build/builder/core.rs	Updates test call sites to include the new adaptive_l parameter.
diskann-benchmark/src/backend/disk_index/search.rs	Passes None for the new adaptive_l argument (not yet exposed via benchmark JSON).

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[magdalendobson]

You may want to take a look at the changes that are coming to filters with #1141 and make sure your changes are compatible

[wuw92]

Worth noting this whole module diskann-tools/src/utils/search_disk_index.r looks dead. pub fn search_disk_index / SearchDiskIndexParameters aren't referenced from any binary.
I recommend deleting search_disk_index.rs (and its pub mod / pub use in utils/mod.rs) in a follow-up rather than carry the filter search migration.

[wuw92]

nit: Plan  tends to read as a query/execution plan: something the engine generates and optimize. Consdier naming SearchMode  or  SearchKind  which would line up more directly with what the variants express