`env_logger` should not be a dependency of `cozo-core`

[jakoschiko]

Currently env_logger is a dependency of cozo-core. But it's only initialized in tests and the binary.

> rg env_logger
Cargo.lock
773: "env_logger",
832: "env_logger",
1272:name = "env_logger"

cozo-core/src/runtime/tests.rs
75:    let _ = env_logger::builder().is_test(true).try_init();
94:    let _ = env_logger::builder().is_test(true).try_init();
124:    let _ = env_logger::builder().is_test(true).try_init();

cozo-bin/src/main.rs
14:use env_logger::Env;
40:            env_logger::Builder::from_env(Env::default().default_filter_or("info")).init();

cozo-bin/Cargo.toml
47:env_logger = "0.11.3"

cozo-core/Cargo.toml
93:env_logger = "0.11.3"

cozo-core/tests/air_routes.rs
15:use env_logger::Env;
23:        env_logger::Builder::from_env(Env::default().default_filter_or("info")).init();

So I assume it could be a dev-dependency for cozo-core and a normal dependency for cozo-bin.