refactor: moved pypi installation into its own module (#589)

Refactored the pypi environment installation code into it's own module.

#601 depends on this.

src/cli/completion.rs

@@ -84,7 +84,7 @@ mod tests {
 
     #[test]
     pub fn test_zsh_completion() {
-        let mut script = r#"
+        let script = r#"
 (add)
 _arguments "${_arguments_options[@]}" \
 '--manifest-path=[The path to '\''pixi.toml'\'']:MANIFEST_PATH:_files' \
@@ -120,7 +120,7 @@ _arguments "${_arguments_options[@]}" \
 ;;
 
         "#;
-        let result = replace_zsh_completion(&mut script);
+        let result = replace_zsh_completion(script);
         insta::assert_snapshot!(result);
     }
 

src/cli/init.rs

@@ -236,7 +236,7 @@ mod tests {
         assert_eq!(read_file_content(&file_path), original_content);
 
         // Scenario 4: Path is a folder not a file, give an error.
-        assert!(create_or_append_file(&dir.path(), template).is_err());
+        assert!(create_or_append_file(dir.path(), template).is_err());
 
         dir.close().unwrap();
     }