refactor: Remove redundant ValueSet call and convert global function to private method

- TestsController: Remove duplicate rangeTypeOptions assignment that was being
  set inside the NUM condition block, causing it to be set unnecessarily
  when it's also handled elsewhere

- ResponseTrait: Convert global helper function convert_empty_strings_to_null()
  to private class method convertEmptyStringsToNull() for better encapsulation
  and to avoid dependency on global functions

- Database schema: Update clqms_database.dbml with accurate table structure
  derived from app/Models/ directory, reorganizing tables by functional
  categories (Patient, Visit, Organization, Location, Test, Specimen,
  Order, Contact management)

app/Controllers/TestsController.php

@@ -184,7 +184,6 @@ class TestsController extends BaseController
                         ];
                     }, $refnumData ?? []);
 
-                    $row['rangeTypeOptions'] = ValueSet::getOptions('range_type');
                 }
 
                 if ($refType === '2' || $refType === 'TEXT' || $refType === '4' || $refType === 'VSET') {

app/Traits/ResponseTrait.php

@@ -23,9 +23,41 @@ trait ResponseTrait
     {
         // Convert empty strings to null in the data
         if ($data !== null && (is_array($data) || is_object($data))) {
-            $data = convert_empty_strings_to_null($data);
+            $data = $this->convertEmptyStringsToNull($data);
         }
         
         return $this->baseRespond($data, $status, $message);
     }
+
+    /**
+     * Recursively convert empty strings to null in arrays or objects
+     * 
+     * @param mixed $data The data to process (array, object, or scalar)
+     * @return mixed The processed data with empty strings converted to null
+     */
+    private function convertEmptyStringsToNull($data)
+    {
+        if (is_array($data)) {
+            foreach ($data as $key => $value) {
+                if (is_array($value)) {
+                    $data[$key] = $this->convertEmptyStringsToNull($value);
+                } elseif (is_object($value)) {
+                    $data[$key] = $this->convertEmptyStringsToNull($value);
+                } elseif ($value === '') {
+                    $data[$key] = null;
+                }
+            }
+        } elseif (is_object($data)) {
+            foreach ($data as $key => $value) {
+                if (is_array($value)) {
+                    $data->$key = $this->convertEmptyStringsToNull($value);
+                } elseif (is_object($value)) {
+                    $data->$key = $this->convertEmptyStringsToNull($value);
+                } elseif ($value === '') {
+                    $data->$key = null;
+                }
+            }
+        }
+        return $data;
+    }
 }