Fix EqualsFilter to handle compound indexes correctly

The numeric path in applyOnIndex now properly handles both single-field
indexes (List) and compound indexes (NavigableMap) using processIndexValue.
This fixes the test failures in CollectionCompoundIndexTest.testIssue178
and RepositorySearchTest.testFindByEntityId.

Co-authored-by: anidotnet <696662+anidotnet@users.noreply.github.com>

Author: Copilot

nitrite/src/main/java/org/dizitart/no2/filters/EqualsFilter.java

@@ -43,22 +43,25 @@ public boolean apply(Pair<NitriteId, Document> element) {
 
     @Override
     public List<?> applyOnIndex(IndexMap indexMap) {
-        List<NitriteId> nitriteIds = new ArrayList<>();
-        
         // If value is a Number, we need to check for numeric equivalents across types
         // Otherwise, use fast direct lookup
         if (getValue() instanceof Number) {
             // Scan for all numerically equivalent values
+            List<java.util.NavigableMap<Comparable<?>, Object>> subMaps = new ArrayList<>();
+            List<NitriteId> nitriteIds = new ArrayList<>();
+            
             for (Pair<Comparable<?>, ?> entry : indexMap.entries()) {
                 if (deepEquals(getValue(), entry.getFirst())) {
                     Object entryValue = entry.getSecond();
-                    if (entryValue instanceof List) {
-                        @SuppressWarnings("unchecked")
-                        List<NitriteId> result = (List<NitriteId>) entryValue;
-                        nitriteIds.addAll(result);
-                    }
+                    // Handle both single-field indexes (List) and compound indexes (NavigableMap)
+                    processIndexValue(entryValue, subMaps, nitriteIds);
                 }
             }
+            
+            // Return sub-maps for compound indexes, or nitrite IDs for single-field indexes
+            if (!subMaps.isEmpty()) {
+                return subMaps;
+            }
             return nitriteIds;
         }