test: rust decoding test for cpp-encoded result (#31)

Context:
- As we develop the native Rust implementation, we need a way to ensure
the results match those from the benchmark C++ implementation.

Implemented:
- Added `test_rust_decompresses_cpp_encoded_data` to verify end-to-end
decoding using deterministic input with varied bit patterns for better
coverage.

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: Weixing-Zhang

tests/cpp_compat_tests.rs

@@ -0,0 +1,46 @@
+#![cfg(all(feature = "rust", feature = "cpp"))]
+
+use fastpfor::cpp::Codec32 as _;
+use fastpfor::rust::Integer as _;
+use fastpfor::{cpp, rust};
+use std::io::Cursor;
+
+#[test]
+fn test_rust_decompresses_cpp_encoded_data() {
+    let input: Vec<u32> = (0..256).map(|i| (i * 32) ^ (i >> 1)).collect();
+
+    // Buffer for the C++ encoded
+    let mut compressed_buffer = vec![0; input.len()];
+
+    // C++ encoding
+    let codec_cpp = cpp::FastPFor128Codec::new();
+    let encoded_cpp = codec_cpp.encode32(&input, &mut compressed_buffer).unwrap();
+    let compressed_len = encoded_cpp.len();
+
+    // C++ decoding
+    let mut decoded_by_cpp = vec![0; input.len()];
+    let decoded_cpp = codec_cpp
+        .decode32(encoded_cpp, &mut decoded_by_cpp)
+        .unwrap();
+
+    // Rust decoding
+    let mut input_offset = Cursor::new(0u32);
+    let mut codec_rs = rust::FastPFOR::new(rust::DEFAULT_PAGE_SIZE, rust::BLOCK_SIZE_128);
+    let mut decoded_by_rust = vec![0; input.len()];
+    codec_rs
+        .uncompress(
+            &compressed_buffer,
+            compressed_len as u32,
+            &mut input_offset,
+            &mut decoded_by_rust,
+            &mut Cursor::new(0u32),
+        )
+        .unwrap();
+
+    assert_eq!(
+        decoded_cpp.len(),
+        decoded_by_rust.len(),
+        "Mismatched output lengths"
+    );
+    assert_eq!(decoded_cpp, decoded_by_rust);
+}