feat: support prefilter

[silver-ymz]

close #27

Add a new guc bm25_catalog.enable_prefilter. It will pushdown the where clause to index process. And index will check it before calculating bm25 score.

• bm25_catalog.enable_prefilter is default true.
• You can see tests/sqllogictest/prefilter.slt as an example.

[Copilot]

Pull Request Overview

This PR adds a new prefilter feature to the BM25 catalog extension that pushes WHERE clause filters down to the index scanning process, allowing conditions to be evaluated before computing BM25 scores.

• Adds a new GUC parameter bm25_catalog.enable_prefilter (default: true) to control prefiltering
• Implements a PostgreSQL executor hook to capture scan state and enable filter evaluation during index scans
• Integrates prefilter functionality into the block_wand algorithms to check conditions before scoring documents

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/sqllogictest/prefilter.slt	Test file demonstrating prefilter functionality with different settings
src/segment/field_norm.rs	Updated lifetime annotation for memory reader method
src/index/scan.rs	Major changes to scanner state management and prefilter implementation
src/index/mod.rs	Added hook module initialization
src/index/hook.rs	New PostgreSQL executor hook implementation for prefilter support
src/guc.rs	Added ENABLE_PREFILTER GUC setting configuration
src/datatype/text_bm25vector.rs	Minor string formatting improvements
src/datatype/memory_bm25vector.rs	Updated lifetime annotation for borrow method
src/datatype/functions.rs	Simplified negation expression
src/algorithm/block_wand.rs	Added filter parameter to block_wand algorithms

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[Copilot]

Commented-out code should be removed unless it serves a specific purpose. If this is needed for future PostgreSQL version compatibility, add a clear comment explaining the purpose and expected timeline for usage.

Suggested change

	// #[cfg(feature = "pg18")]
	// #[cfg(feature = "pg18")]
	// The following line is required for PostgreSQL 18+ compatibility.
	// Uncomment when upgrading to PostgreSQL 18 or enabling the "pg18" feature.

[Copilot]

The logic for returning true when the state is null should be documented. It's not immediately clear why a null state should be considered as passing the boolean qualification check.

Suggested change

	use pgrx::PgMemoryContexts;
	use pgrx::PgMemoryContexts;
	// If the qualification state is null, there are no conditions to check,
	// so the qualification passes by default. This follows PostgreSQL convention.

[Copilot]

Similar to the previous comment, returning true for a null node should be documented to explain why this represents a valid/passing condition for the check function.

Suggested change

	unsafe fn check(node: *mut pgrx::pg_sys::IndexScanState, p: pgrx::pg_sys::ItemPointer) -> bool {
	unsafe fn check(node: *mut pgrx::pg_sys::IndexScanState, p: pgrx::pg_sys::ItemPointer) -> bool {
	// If the scan state node is null, there are no conditions to check,
	// so we return true to indicate a passing/valid condition.