Filter callback interface for on-the-fly KNN filtering

[sanikolaev]

This commit introduces a filter callback mechanism that allows external code to pass filter callbacks to the KNN library without creating a direct dependency on hnswlib headers in the public API.

Related PRs:

• hnswlib - On-the-fly filtering for KNN search hnswlib#1
• daemon - On-the-fly filtering for KNN (prototype, WIP) manticoresearch#4129

Key changes:

• Bumped LIB_VERSION from 9 to 10 to reflect API changes
• Added FilterCallback_fn type alias (std::function<bool(uint32_t)>) as a public API for filter callbacks
• Added forward declaration for hnswlib::BaseFilterFunctor in global namespace to avoid including hnswlib headers in public API
• Created FilterCallbackWrapper_c class that adapts FilterCallback_fn to hnswlib::BaseFilterFunctor internally
• Updated KNN_i::CreateIterator() to accept both:
  • ::hnswlib::BaseFilterFunctor * pFilter (for internal use)
  • FilterCallback_fn fnFilter (for public API)
• Updated KNNIndex_i::Search() to accept both filter types and use the wrapper when fnFilter is provided but pFilter is null
• Updated CreateIterator() function to accept and pass both filter types
• Changed all hnswlib:: namespace references to ::hnswlib:: for explicit global namespace qualification

Architecture:
External code creates a function/lambda implementing the filter logic and passes it as FilterCallback_fn to the KNN library. The KNN library then wraps this in FilterCallbackWrapper_c which inherits from hnswlib::BaseFilterFunctor, allowing it to be passed to hnswlib's search algorithm. This maintains API separation while enabling on-the-fly filtering functionality.

This change enables on-the-fly KNN filtering where the search algorithm continues exploring until k filtered candidates are found, rather than finding k total candidates and then filtering them post-search.

Notes

This PR includes a temporary change in cmake/GetHNSW.cmake. It points to an updated version of hnswlib in a branch and will be updated later.

[github-actions]

Windows test results

  5 files    5 suites   18m 6s ⏱️
482 tests 467 ✅ 14 💤 1 ❌
490 runs  475 ✅ 14 💤 1 ❌

For more details on these failures, see this check.

Results for commit 920f181.

[github-actions]

Linux debug test results

  8 files    8 suites   13m 1s ⏱️
501 tests 480 ✅ 21 💤 0 ❌
515 runs  494 ✅ 21 💤 0 ❌

Results for commit 920f181.

[github-actions]

Linux release test results

  8 files    8 suites   6m 56s ⏱️
501 tests 486 ✅ 14 💤 1 ❌
515 runs  500 ✅ 14 💤 1 ❌

For more details on these failures, see this check.

Results for commit 920f181.