feat(snapshot): Allow overriding huge-page configuration on restore

[lisasgoh]

Changes

Closes #6036

Add an optional huge_pages override to PUT /snapshot/load.

• Supports None, Transparent, and 2M.
• Preserves the snapshot’s configuration when omitted.
• Rejects 2M with file-backed restore; UFFD is required.

Reason

Host page configuration does not affect guest-visible snapshot contents. Allowing it to be selected during restore avoids creating duplicate snapshots for each desired backing-page configuration.

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• This functionality cannot be added in rust-vmm.