Create a new transaction definition with a nested field schema, customer link declarations, and optional non-client-scoped partitions. Leaf field values must be one of: "string", "number", "ipAddress", "date", "array", "country". Array fields accept only primitive elements (string, number, boolean, null). "country" values must be ISO 3166-1 alpha-2 codes. Each link txPath and partition txPath must resolve to a declared leaf field (link and partition paths may not target array fields). A link may declare an optional mergeTxPath, which must resolve to an "array" leaf field. Partition types must not collide with link types.