fix: resolve compression_engine import paths in tests

Co-authored-by: aider (openai/andrew/openrouter/qwen/qwen3-coder) <aider@aider.chat>

src/tests.rs

@@ -4,6 +4,7 @@
 mod tests {
     use tempfile::tempdir;
     use std::io::Write;
+    use std::str::FromStr;
     
     // Import the modules we need for testing
     use crate::compression_engine::{self, CompressionType};