MB-69881: Re-architect vector search

[CascadingRadium]

• Adapt to new SegmentEligibleDocuments interface which allows usage of visitor-pattern based iteration of eligible documents for filtered vector search.

[Copilot]

Pull request overview

This PR refactors the vector search architecture to adopt a visitor-pattern based iteration model for eligible documents in filtered vector searches. The change adapts the existing code to implement the new SegmentEligibleDocuments interface from the bleve_index_api package.

Key Changes:

• Replaced direct slice return (SegmentEligibleDocs) with an iterator-based approach (SegmentEligibleDocuments)
• Introduced eligibleDocumentList and eligibleDocumentIterator types to support the new visitor pattern
• Updated VectorReader to use the new Count() method instead of directly checking slice length

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

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[coveralls]

Pull Request Test Coverage Report for Build 20851311548

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 85.464%

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Totals
Change from base Build 19180002944:	0.0%
Covered Lines:	488
Relevant Lines:	571

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💛 - Coveralls