feat: swap println for eprintln or debug_eprintln

Unified expected output to always eprintln so outputs can be piped to
other processes. Added debug_eprintln and switched all occurances of
debug_println.

src/command_builder.rs

@@ -9,7 +9,7 @@ use std::{
     process::{Child, Command, Stdio},
 };
 
-use crate::debug_println;
+use crate::debug_eprintln;
 
 pub struct Args(Vec<String>);
 
@@ -64,7 +64,7 @@ impl CommandBuilder {
     }
 
     pub fn build(self) -> Result<Command> {
-        debug_println!("-----\n{self}\n-----");
+        debug_eprintln!("-----\n{self}\n-----");
 
         let (first, rest) = self.args.split_first().context("empty args")?;
         let mut command = Command::new(first);