minor #53963 [Uid] Optimize UuidV4 generation (smnandre)

This PR was squashed before being merged into the 7.1 branch.

Discussion
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[Uid] Optimize UuidV4 generation

| Q             | A
| ------------- | ---
| Branch?       | 7.1
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        | Fix #
| License       | MIT

I tried to optimize as much as I could the [UuidV4 generation](https://github.com/symfony/symfony/blob/7.1/src/Symfony/Component/Uid/UuidV4.php).

According to local tests, the code is now between `35%` and `40%` faster.

(But to be fair... we are talking nanoseconds here 😅)

Thanks `@nicolas`-grekas for the help in this ~~useless~~ fun quest  😃

--

--> Bench (& results): https://github.com/smnandre/uuid-bench

Commits
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7b5c57b [Uid] Optimize UuidV4 generation

src/Symfony/Component/Uid/UuidV4.php

@@ -23,12 +23,19 @@ class UuidV4 extends Uuid
     public function __construct(?string $uuid = null)
     {
         if (null === $uuid) {
-            $uuid = random_bytes(16);
-            $uuid[6] = $uuid[6] & "\x0F" | "\x40";
-            $uuid[8] = $uuid[8] & "\x3F" | "\x80";
-            $uuid = bin2hex($uuid);
-
-            $this->uid = substr($uuid, 0, 8).'-'.substr($uuid, 8, 4).'-'.substr($uuid, 12, 4).'-'.substr($uuid, 16, 4).'-'.substr($uuid, 20, 12);
+            // Generate 36 random hex characters (144 bits)
+            // xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+            $uuid = bin2hex(random_bytes(18));
+            // Insert dashes to match the UUID format
+            // xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
+            $uuid[8] = $uuid[13] = $uuid[18] = $uuid[23] = '-';
+            // Set the UUID version to 4
+            // xxxxxxxx-xxxx-4xxx-xxxx-xxxxxxxxxxxx
+            $uuid[14] = '4';
+            // Set the UUID variant: the 19th char must be in [8, 9, a, b]
+            // xxxxxxxx-xxxx-4xxx-?xxx-xxxxxxxxxxxx
+            $uuid[19] = ['8', '9', 'a', 'b', '8', '9', 'a', 'b', 'c' => '8', 'd' => '9', 'e' => 'a', 'f' => 'b'][$uuid[19]] ?? $uuid[19];
+            $this->uid = $uuid;
         } else {
             parent::__construct($uuid, true);
         }