make `raw_continue_iterable_query` private

[mversic]

is there a reason to have it public?

_Originally posted by @mversic in https://github.com/hyperledger/iroha/pull/4833#discussion_r1680992768_

[mversic]

maybe we can use serialize/deserialize trick like in wasm_samples/query_assets_and_save_cursor/src/lib.rs