Update user properties

Set or unset first-party properties for a wallet profile. Override display name, email, socials, avatar, location, and other identity fields. Send null as a value to delete (unset) that property: the field then reads as null everywhere, including over any globally-enriched fallback value, until a new value is set. user_id cannot be unset (it participates in identity stitching). Set-and-unset compose in a single call. Note: profile enrichment snapshots are versioned, but first-party property overrides (and their deletions) are always current; a point-in-time read (timestamp) reflects the latest overrides, so a deletion also masks historical reads.