Disable graph search pruning

[tlwillke]

• Forward-port of the fix from Disable TopK/filtered pruning, preserve legacy threshold behavior #682 (originally resolving Search pruning via usePruning can be too aggressive for non-hierarchical graph indices #678).
• Added comments for clarity

[github-actions]

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[jshook]

nothing found of concern

[ashkrisk]

Resolves #678