MB-65018 add custom_filter/custom_score query nodes with context-driven callback hooks

[maneuvertomars]

This PR adds two new query node types in Bleve: custom_filter and custom_score, both wrapping an inner query.
Execution is embedding-driven via request-scoped context hooks (CustomFilterFactory / CustomScoreFactory) so Bleve remains engine-agnostic.
custom_filter applies per-hit keep/drop logic through FilteringSearcher; custom_score applies per-hit score mutation through ScoreMutatingSearcher.

[coveralls]

coverage: 52.25% (-0.4%) from 52.691% — MB-65018 into master

[abhinavdangeti]

@maneuvertomars Let's make sure you scrub the proposed code once again for any nil handling, especially around pointer dereferencing.

[abhinavdangeti]

@maneuvertomars Let's do a quick walk through tomorrow.

[abhinavdangeti]

Please wait for review from @CascadingRadium as well.

[capemox]

@maneuvertomars please add functions to create new custom_filter/custom_score queries in query.go in bleve's root, and also add end to end tests in search_test.go to validate it works with some non-trivial custom filters and custom scorers.

[abhinavdangeti]

@maneuvertomars lets also capture the behavior in the .md when the user does not enable docValues for the necessary field mappings.

[abhinavdangeti]

use doc values instead of stored fields for custom query field loading

Looks like you already covered this with your last patch 👍🏼

[Copilot]

Pull request overview

Adds first-class custom_filter and custom_score query nodes that allow embedders to inject per-hit filtering and score mutation logic, while keeping Bleve core engine-agnostic and enabling optional doc-values-backed field access within callbacks.

Changes:

• Introduces CustomFilterQuery / CustomScoreQuery JSON node support (via pluggable parsers) and corresponding searchers.
• Implements doc value loading + field-type-aware decoding to populate DocumentMatch.Fields before invoking callbacks.
• Adds unit/integration tests and user-facing documentation for custom query behavior and requirements.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
search/searcher/search_custom_score.go	Adds a searcher wrapper that loads doc values and mutates hit scores via a callback.
search/searcher/search_custom_filter.go	Adds a searcher wrapper that loads doc values and applies a per-hit accept/drop callback.
search/searcher/search_custom_fields.go	Adds shared helpers to load doc values and decode them into typed DocumentMatch.Fields.
search/query/query.go	Extends ParseQuery to recognize custom_filter / custom_score nodes and delegate to embedder-registered parsers.
search/query/custom_score.go	Adds CustomScoreQuery type, JSON marshaling, validation, and searcher construction.
search/query/custom_filter.go	Adds CustomFilterQuery type, JSON marshaling, validation, and searcher construction.
search/query/custom_payload.go	Adds shared payload unmarshaling and mapping-type resolution utilities.
search/query/custom_query_test.go	Adds JSON marshal/unmarshal tests for both custom query types.
search_test.go	Adds end-to-end tests verifying filtering/scoring behavior and doc-values field decoding.
docs/custom_query.md	Adds documentation describing custom query nodes, payload semantics, and doc-values requirements.

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[capemox]

Few more tiny changes @maneuvertomars, otherwise looks alright to me!

[capemox]

Also @maneuvertomars please do click "resolve conversation" for the comments that you've taken care of, it's easier for everyone

Addressed comments, approved by others.