Move ArtiConfig to new arti::cfg module

Cargo.lock

crates/arti-bench/Cargo.toml

crates/arti-bench/src/main.rs

crates/arti-config/src/lib.rs

crates/arti-config/src/options.rs

crates/arti-testing/Cargo.toml

crates/arti-testing/src/main.rs

crates/arti/Cargo.toml

crates/arti/src/cfg.rs

crates/arti/src/lib.rs

crates/arti/src/watch_cfg.rs