Resolves a batch of identifiers (ISIN, CUSIP, symbol) and returns one
result per identifier, keyed by the identifier exactly as sent.

Each identifier is looked up the same way GET /v1/security/{id} looks up
one: identifiers are matched verbatim, so a lowercase symbol is
not_found. Asset-type caches are consulted in the order given by
resolution_order (or the default order when omitted), and asset types
not listed are not searched.