Support the KNN shard-ratio feature

[mgravell]

from 8.6.1, FT.HYBRID KNN has a new SHARD_K_RATIO feature: RediSearch/RediSearch#8227

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Note

Medium Risk
Adds a new KNN query parameter that affects search execution and modifies the public API surface for VectorSearchMethod.NearestNeighbour, which could impact consumers and query behavior. Test skipping logic was also adjusted to defer version checks, which could hide/alter CI coverage if misused.

Overview
Adds support for Redis 8.6.1+ FT.HYBRID KNN SHARD_K_RATIO by extending VectorSearchMethod.NearestNeighbour with an optional shardRatio and emitting SHARD_K_RATIO in the generated argument list.

Updates the shipped/unshipped public API to reflect the new overload while retaining a binary-compat NearestNeighbour(int, int?) signature, and expands unit/integration tests to cover shard-ratio scenarios plus adds deferVersionCheck/overrideVersion paths to make version-based skips rely on detected server version.

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[jit-ci]

🛡️ Jit Security Scan Results

✅ No security findings were detected in this PR

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