Feature Request: Server-side Proto Key Discovery Commands

Feature Request: Server-side Proto Key Discovery Commands: a task in LegoFlow-SWE (Harbor dataset). Currently, locating protobuf keys by type or by a specific field value requires a full SCAN followed by a per-key PROTO.GETFIELD loop executed on the client. This is inefficient for large datasets…

The task

Currently, locating protobuf keys by type or by a specific field value requires a full `SCAN` followed by a per-key `PROTO.GETFIELD` loop executed on the client. This is inefficient for large datasets or when only a subset of keys is needed. We need two new server-side commands to perform this filtering efficiently.

Part of Lego-X/LegoFlow-SWE.