Returns holding records ordered oldest first by createdAt. sort accepts only
createdAt:asc — the one order this endpoint's keyset pagination can serve; any other
value, including the shared parameter's createdAt:desc default, is rejected with
400. A holding
with status: open is a live position; status: closed means the record was superseded
by a transfer or burn and is retained for reconciliation.

A locked holding (isLocked: true) is reserved against an in-flight transfer
instruction and cannot fund another one until that instruction settles or
expires. lockExpiresAt tells you when a lock lapses without anyone acting, which
is what distinguishes a settlement in progress from one that has stalled.

This endpoint reads the token standard's interface view, so it returns holdings of
every compliant asset — DTCC securities and Canton Coin alike. Where the dtcc tier
is also licensed, registry-specific fields (instrumentScheme, label) are added to
the same records. Summing amount across a party's open holdings for one instrument
gives that party's position; include locked holdings in the total, since a
lock reserves a position rather than removing it.