Restore MIXTURE to Phase 2 algorithm set

MIXTURE uses a neutral selection strategy (rule-based only, no MAX/MIN
bias) and a unique isomorphism pre-check, making it algorithmically
distinct from MAX and MIN. It serves as the fallback for reactions where
neither maximum nor minimum overlap bias resolves the mapping cleanly.

The selection comparator gives MIXTURE lowest priority so it only wins
when it produces better coverage/quality than the other three — restoring
it cannot degrade results on reactions where RINGS/MIN/MAX succeed.

Author: asad

src/main/java/com/bioinceptionlabs/reactionblast/mapping/CallableAtomMappingTool.java

@@ -175,13 +175,13 @@ private void generateAtomAtomMapping(
         boolean ringsAlreadyRun = solution.containsKey(RINGS);
         IMappingAlgorithm[] remaining;
         if (minAlreadyRun && ringsAlreadyRun) {
-            remaining = new IMappingAlgorithm[]{MAX};
+            remaining = new IMappingAlgorithm[]{MAX, MIXTURE};
         } else if (minAlreadyRun) {
-            remaining = new IMappingAlgorithm[]{MAX, RINGS};
+            remaining = new IMappingAlgorithm[]{MAX, MIXTURE, RINGS};
         } else if (ringsAlreadyRun) {
-            remaining = new IMappingAlgorithm[]{MIN, MAX};
+            remaining = new IMappingAlgorithm[]{MIN, MAX, MIXTURE};
         } else {
-            remaining = new IMappingAlgorithm[]{MIN, MAX, RINGS};
+            remaining = new IMappingAlgorithm[]{MIN, MAX, MIXTURE, RINGS};
         }
 
         try {