[ref] bc-db: merge db handler and reader into a struct

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

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

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

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

...dules/blockchain/bc-db-writer/src/indexes/transactions.rs

lib/modules/blockchain/bc-db-writer/src/lib.rs

lib/modules/blockchain/blockchain/src/fork/fork_algo.rs

lib/modules/blockchain/blockchain/src/fork/rollback.rs

lib/modules/blockchain/blockchain/tests/common.rs

lib/modules/gva/src/db.rs

lib/modules/gva/src/schema/entities/block.rs

lib/modules/gva/src/schema/queries/block.rs

lib/modules/gva/src/schema/queries/blocks.rs

lib/modules/gva/src/schema/queries/current.rs

lib/tools/common-tools/src/traits/mod.rs

lib/tools/dbs-tools/Cargo.toml

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

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