[ref] bc-db-reader: implement mock feature & declare client-indexer

Cargo.lock

lib/modules-lib/bc-db-reader/Cargo.toml

lib/modules-lib/bc-db-reader/src/lib.rs

lib/modules-lib/bc-db-reader/src/trait.rs

lib/tools/dbs-tools/Cargo.toml

lib/tools/dbs-tools/src/errors.rs

lib/tools/dbs-tools/src/kv_db/file.rs