refactor: finalize DiskANN, OPQ, and compaction modules

Late-completing agents produced cleaner implementations. All 40 tests
pass across diskann (13), opq (11), and compaction (16) modules.

https://claude.ai/code/session_01ERu5fZkBsXL4KSfCpTJvfx

Author: claude

crates/ruvector-core/src/advanced_features.rs

@@ -10,6 +10,7 @@
 //! - Matryoshka Representation Learning (adaptive-dimension search)
 //! - Optimized Product Quantization (OPQ) with learned rotation matrix
 
+pub mod compaction;
 pub mod conformal_prediction;
 pub mod diskann;
 pub mod filtered_search;
@@ -44,3 +45,6 @@ pub use sparse_vector::{
 pub use diskann::{
     DiskIndex, DiskNode, IOStats, MedoidFinder, PageCache, VamanaConfig, VamanaGraph,
 };
+pub use compaction::{
+    BloomFilter, CompactionConfig, LSMIndex, LSMStats, MemTable, Segment,
+};