Improves level of theory matching in Arkane

Updates Arkane's level of theory matching logic to prioritize entries with the latest year when no target year is specified.

This ensures that the most up-to-date level of theory is selected
when multiple options are available.

Author: calvinp0

arc/statmech/arkane.py

@@ -850,6 +850,7 @@ def _find_best_level_key_for_sp_level(level: "Level",
     target_software = level.software.lower() if level.software else None
 
     best_key = None
+    best_year = None
 
     for lot_str in _iter_level_keys_from_section(file_path, section_start, section_end):
         params = _parse_lot_params(lot_str)
@@ -884,10 +885,16 @@ def _find_best_level_key_for_sp_level(level: "Level",
                 continue
             best_key = lot_str
             break
-        else:
-            if cand_year is None:
+
+        # No target year specified: pick the latest year if present, otherwise fall back to no-year entry.
+        if cand_year is None:
+            if best_year is None:
                 best_key = lot_str
-                break
+            continue
+
+        if best_year is None or cand_year > best_year:
+            best_year = cand_year
+            best_key = lot_str
 
     return best_key