[tests] gva: deep refactor to make the code testable

.gitlab-ci.yml

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

lib/modules/gva/Cargo.toml

lib/modules/gva/src/context.rs

lib/modules/gva/src/db.rs

lib/modules/gva/src/graphql.rs

lib/modules/gva/src/lib.rs

lib/modules/gva/src/schema.rs

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

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

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

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

lib/modules/gva/src/webserver.rs