Sorting: Renamed sort set to sort rule

Renamed based on feedback from Tim and Script on Discord.
Also fixed flaky test

app/Sorting/SortRuleOperation.php

@@ -0,0 +1,68 @@
+<?php
+
+namespace BookStack\Sorting;
+
+use Closure;
+use Illuminate\Support\Str;
+
+enum SortRuleOperation: string
+{
+    case NameAsc = 'name_asc';
+    case NameDesc = 'name_desc';
+    case NameNumericAsc = 'name_numeric_asc';
+    case CreatedDateAsc = 'created_date_asc';
+    case CreatedDateDesc = 'created_date_desc';
+    case UpdateDateAsc = 'updated_date_asc';
+    case UpdateDateDesc = 'updated_date_desc';
+    case ChaptersFirst = 'chapters_first';
+    case ChaptersLast = 'chapters_last';
+
+    /**
+     * Provide a translated label string for this option.
+     */
+    public function getLabel(): string
+    {
+        $key = $this->value;
+        $label = '';
+        if (str_ends_with($key, '_asc')) {
+            $key = substr($key, 0, -4);
+            $label = trans('settings.sort_rule_op_asc');
+        } elseif (str_ends_with($key, '_desc')) {
+            $key = substr($key, 0, -5);
+            $label = trans('settings.sort_rule_op_desc');
+        }
+
+        $label = trans('settings.sort_rule_op_' . $key) . ' ' . $label;
+        return trim($label);
+    }
+
+    public function getSortFunction(): callable
+    {
+        $camelValue = Str::camel($this->value);
+        return SortSetOperationComparisons::$camelValue(...);
+    }
+
+    /**
+     * @return SortRuleOperation[]
+     */
+    public static function allExcluding(array $operations): array
+    {
+        $all = SortRuleOperation::cases();
+        $filtered = array_filter($all, function (SortRuleOperation $operation) use ($operations) {
+            return !in_array($operation, $operations);
+        });
+        return array_values($filtered);
+    }
+
+    /**
+     * Create a set of operations from a string sequence representation.
+     * (values seperated by commas).
+     * @return SortRuleOperation[]
+     */
+    public static function fromSequence(string $sequence): array
+    {
+        $strOptions = explode(',', $sequence);
+        $options = array_map(fn ($val) => SortRuleOperation::tryFrom($val), $strOptions);
+        return array_filter($options);
+    }
+}