redisvector: fix score threshold option

[acrmp]

• Redis vector range queries expect a radius rather than a score threshold.
• The existing code passed the score threshold through directly as the radius param. This means that a higher score threshold will result in in more matches than a lower score threshold which seems wrong. Instead this PR subtracts the score threshold from 1.
• The langchain project appears to have deprecated score threshold in favour of distance threshold. A future improvement would be to add a WithDistanceThreshold option for consistency.
• This PR is a breaking change for clients using redisvector and WithScoreThreshold. An alternative would be to keep the existing behaviour but add WithDistanceThreshold and guide users towards it.

PR Checklist

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• Contains test coverage for new functions.
• Passes all golangci-lint checks. - There are some existing complaints about magic numbers not introduced by this PR.

[tmc]

Bit on the fence about a breaking change but this seems more appropriate, in general.

[tmc]

Could you tackle the WithDistanceThreshold, that sounds like a nice option.

[tmc]

LGTM