perf: memoize PriceReliability + PriceClassification per row

Audit item #10. PriceReliability::fromUpdatedAt was being invoked
~10× per station per /api/stations response — twice in the sort
comparator (once for $a, once for $b), once in the count groupBy, and
once per resource render. PriceClassification::fromUpdatedAt was
called twice inside the resource (value + label).

The controller now computes the parsed datetime + reliability +
classification once per row and stashes them on the row. Sort,
groupBy, and StationResource read the cached values; the resource
keeps a fresh-compute fallback for callers that bypass the controller.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/Http/Controllers/Api/StationController.php

@@ -2,6 +2,7 @@
 
 namespace App\Http\Controllers\Api;
 
+use App\Enums\PriceClassification;
 use App\Enums\PriceReliability;
 use App\Http\Controllers\Controller;
 use App\Http\Requests\Api\NearbyStationsRequest;
@@ -59,19 +60,23 @@ class StationController extends Controller
             ->where('stations.permanent_closure', false)
             ->get();
 
+        // Compute reliability + classification once per row. The resource and
+        // sort/groupBy below all read these cached attributes — without this,
+        // PriceReliability::fromUpdatedAt is invoked ~10× per station per
+        // response (sort comparator, count groupBy, resource value+label).
+        $all->each(function ($s): void {
+            $updatedAt = $s->price_effective_at ? Carbon::parse($s->price_effective_at) : null;
+            $s->_updated_at = $updatedAt;
+            $s->_reliability = PriceReliability::fromUpdatedAt($updatedAt);
+            $s->_classification = PriceClassification::fromUpdatedAt($updatedAt);
+        });
+
         $filtered = $all->filter(fn ($s) => (float) $s->distance_km <= $radius);
 
         $stations = $sort === 'reliable'
             ? $filtered
                 ->sort(function ($a, $b) {
-                    $weightA = PriceReliability::fromUpdatedAt(
-                        $a->price_effective_at ? Carbon::parse($a->price_effective_at) : null
-                    )->weight();
-                    $weightB = PriceReliability::fromUpdatedAt(
-                        $b->price_effective_at ? Carbon::parse($b->price_effective_at) : null
-                    )->weight();
-
-                    return $weightA <=> $weightB
+                    return $a->_reliability->weight() <=> $b->_reliability->weight()
                         ?: ((int) $a->price_pence <=> (int) $b->price_pence)
                         ?: ((float) $a->distance_km <=> (float) $b->distance_km);
                 })
@@ -85,9 +90,7 @@ class StationController extends Controller
         $prices = $stations->pluck('price_pence');
 
         $reliabilityCounts = $stations
-            ->groupBy(fn ($s) => PriceReliability::fromUpdatedAt(
-                $s->price_effective_at ? Carbon::parse($s->price_effective_at) : null
-            )->value)
+            ->groupBy(fn ($s) => $s->_reliability->value)
             ->map->count();
 
         Search::create([