Add missing 1.3.1 and 1.4.0 changelog entries

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jensens

CHANGES.md

@@ -1,5 +1,19 @@
 # Changelog
 
+## 1.4.0 (2026-02-24)
+
+- Add `decode_zodb_record_for_pg_json()` — converts ZODB pickle records
+  directly to a JSON string entirely in Rust with the GIL released,
+  eliminating the intermediate Python dict + `json.dumps()` step
+  (1.3x faster full pipeline on real-world data)
+- Restructure BENCHMARKS.md for clarity
+
+## 1.3.1 (2026-02-24)
+
+- Enable thin LTO (`lto = "thin"`) and single codegen unit
+  (`codegen-units = 1`) in Cargo release profile for 6-9% faster
+  decode/encode with no code changes
+
 ## 1.3.0 (2026-02-24)
 
 - Fix SETITEMS/SETITEM/APPENDS/APPEND on dict/list subclasses (OrderedDict,