fix(setnx): use set with nx instead setnx

[ndyakov]

fixes #3715

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Note

Medium Risk
Changes the wire command used by SetNX when expiration==0, which may affect compatibility with very old Redis servers and subtly alter behavior/metrics tied to command names.

Overview
Updates SetNX to always issue SET ... NX (including the zero-expiration case) instead of falling back to the legacy SETNX command.

Removes the deprecation note/compatibility comment that previously justified using SETNX for older Redis versions.

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