Feature request: Efficient prefix exists check

Saw this feature being filed https://github.com/speedb-io/speedb/issues/685. Given speedb is just a fork of rocksdb, rocksdb should be able to implement some efficient way to check if a prefix matches any key in the cf/db?

Start by reviewing the linked Speedb issue and the RocksDB APIs for prefix checks on a column family or database. The issue does not name files or tests, so first establish the expected semantics, performance target, and validation needed for an efficient prefix-existence check.

Written by the indexing model from the issue text.