fix: premature recycles in MGetCache/JsonMGetCache helpers

[rueian]

Note

Medium Risk
Adjusts pooled command buffer lifecycle around DoMultiCache, which can affect concurrency and correctness under load if mishandled. Scope is small but touches low-level client caching/pipelining behavior.

Overview
Fixes a pooling/lifecycle bug in MGetCache and JsonMGetCache where the mgetcachecmds buffer could be returned to mgetcachecmdsp before DoMultiCache finished using it.

doMultiCache now takes the command buffer (instead of a raw slice) and only returns it to the pool after all responses have been processed successfully, avoiding reuse on early exits due to non-Redis errors.

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[jit-ci]

🛡️ Jit Security Scan Results

✅ No security findings were detected in this PR

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^{Security scan by Jit}