Implement xxHash for non-cryptographic use-cases

Let's wait for its merge in core first.

The only place I've found a hash() call is in the Domain entity class:

  /**
   * {@inheritdoc}
   */
  public function createDomainId() {
    // We cannot reliably use sequences (1, 2, 3) because those can be different
    // across environments. Instead, we use the crc32 hash function to create a
    // unique numeric id for each domain. In some systems (Windows?) we have
    // reports of crc32 returning a negative number. Issue #2794047.
    // If we don't use hash(), then crc32() returns different results for 32-
    // and 64-bit systems. On 32-bit systems, the number returned may also be
    // too large for PHP.
    // See #2908236.
    $id = hash('crc32', $this->id());
    $id = abs(hexdec(substr($id, 0, -2)));
    $this->createNumericId($id);
  }

It seems we could replace it by:

/**
 * {@inheritdoc}
 */
public function createDomainId() {
  // Use xxHash instead of CRC32 for better performance and distribution.
  // xxh3 returns a 64-bit hash as hex, stable across platforms.
  // We truncate and convert to a positive integer to ensure portability
  // and compatibility with numeric storage.
  $hash = hash('xxh3', $this->id());        // 64-bit hex string
  $id   = hexdec(substr($hash, 0, 15));     // fits safely in signed 64-bit
  $this->createNumericId($id);
}

@idebr is it what you meant?

Could this be a better solution?

/**
 * Builds a cache key based on the path and options.
 */
protected function buildCacheKey(string $path, array $options): string {
  $normalized = $this->normalizeOptions($options);
  // Use a fast, non-cryptographic hash with excellent distribution.
  return hash(
    'xxh3',
    $path . "\0" . json_encode($normalized, JSON_UNESCAPED_SLASHES)
  );
}

Looks like using serialize() was even more costly than using md5() here.

Switched back to serialize() as it was consistently faster (slightly) after running a few benchmarks.

Can we have an RTBC please?

Merging as the xxh3 version is almost twice as fast as the md5 one.

Thanks @idebr!