fix: use a fixed hash seed for variant hashing, this fixes a bug in v…

…ariant distribution (#179)

src/Stickiness/MurmurHashCalculator.php

@@ -6,8 +6,8 @@
 
 final class MurmurHashCalculator implements StickinessCalculator
 {
-    public function calculate(string $id, string $groupId, int $normalizer = 100): int
+    public function calculate(string $id, string $groupId, int $normalizer = 100, int $seed = 0): int
     {
-        return Murmur::hash3_int("{$groupId}:{$id}") % $normalizer + 1;
+        return Murmur::hash3_int("{$groupId}:{$id}", $seed) % $normalizer + 1;
     }
 }

src/Stickiness/StickinessCalculator.php

@@ -4,5 +4,5 @@
 
 interface StickinessCalculator
 {
-    public function calculate(string $id, string $groupId, int $normalizer = 100): int;
+    public function calculate(string $id, string $groupId, int $normalizer = 100, int $seed = 0): int;
 }

src/Variant/DefaultVariantHandler.php

@@ -11,6 +11,8 @@
 
 final readonly class DefaultVariantHandler implements VariantHandler
 {
+    private const VARIANT_HASH_SEED = 86028157;
+
     public function __construct(
         private StickinessCalculator $stickinessCalculator,
     ) {
@@ -103,7 +105,7 @@ private function calculateStickiness(
                 ?? $this->randomString();
         }
 
-        return $this->stickinessCalculator->calculate($seed, $groupId, $totalWeight);
+        return $this->stickinessCalculator->calculate($seed, $groupId, $totalWeight, $seed = DefaultVariantHandler::VARIANT_HASH_SEED);
     }
 
     private function randomString(): string