[fix] gva: use once_cell to init db handler without unsafe code

Cargo.lock

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

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

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

lib/modules/gva/Cargo.toml

lib/modules/gva/src/context.rs

lib/modules/gva/src/lib.rs

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

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

lib/modules/gva/src/webserver.rs