fix: refactor to avoid circular dependencies

src/main.rs

@@ -1,8 +1,8 @@
 use std::net::IpAddr;
 use std::str::FromStr;
 
-use dsp_thomann::DSP408;
-use dsp_thomann::types;
+use dsp_thomann::dsp408::DSP408;
+use dsp_thomann::dsp408::types;
 
 fn main() -> Result<(), Box<dyn std::error::Error>> {