[fix] kv_typed: iterators must not be reversable at the middle

rust-bins/duniter-dbex/src/migrate.rs

rust-libs/duniter-dbs-read-ops/src/lib.rs

rust-libs/duniter-dbs-write-ops/src/bc/uds.rs

rust-libs/duniter-dbs/Cargo.toml

rust-libs/duniter-dbs/tests/test_read_write.rs

rust-libs/modules/gva/dbs-reader/src/lib.rs

rust-libs/modules/gva/dbs-reader/src/uds_of_pubkey.rs

rust-libs/modules/gva/dbs-reader/src/utxos.rs

rust-libs/tools/kv_typed/src/backend.rs

rust-libs/tools/kv_typed/src/backend/leveldb.rs

rust-libs/tools/kv_typed/src/backend/memory.rs

rust-libs/tools/kv_typed/src/backend/memory_singleton.rs

rust-libs/tools/kv_typed/src/backend/sled.rs

rust-libs/tools/kv_typed/src/collection_ro.rs

rust-libs/tools/kv_typed/src/explorer.rs

rust-libs/tools/kv_typed/src/lib.rs

rust-libs/tools/kv_typed/src/transactional_read.rs

rust-libs/tools/kv_typed/src/transactional_write.rs

rust-libs/tools/kv_typed/tests/test_db_schema.rs