docs: clarify DUMP/RESTORE binary payload usage

[nkaradzhov]

Description

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Checklist

• Does npm test pass with this change (including linting)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?

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Note

Low Risk
Documentation-only changes that clarify how to avoid lossy DUMP payload decoding by mapping blob strings to Buffer; no runtime code or behavior changes.

Overview
Updates the main README and packages/redis/README.md to explicitly call out that commands returning serialized binary payloads (notably DUMP) should be used with BLOB_STRING mapped to Buffer before passing results to RESTORE.

Expands docs/command-options.md with a dedicated DUMP/RESTORE section explaining the failure mode when decoding as string, and shows both withTypeMapping and default commandOptions.typeMapping examples (including a note on v5 vs v4 APIs).

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