HHH-8961  Reduce allocation cost of org.hibernate.cache.spi.CacheKey instances

https://hibernate.atlassian.net/browse/HHH-8961

The report by JOL is now less concerning:

    org.hibernate.cache.spi.CacheKey object internals:
     OFFSET  SIZE         TYPE DESCRIPTION                    VALUE
          0    12              (object header)                N/A
         12     4          int CacheKey.hashCode              N/A
         16     4 Serializable CacheKey.key                   N/A
         20     4         Type CacheKey.type                  N/A
    Instance size: 24 bytes (estimated, the sample instance is not available)
    Space losses: 0 bytes internal + 0 bytes external = 0 bytes total

And when multitenancy is being used:

    org.hibernate.cache.internal.TenantAwareCacheKey object internals:
     OFFSET  SIZE         TYPE DESCRIPTION                    VALUE
          0    12              (object header)                N/A
         12     4          int CacheKey.hashCode              N/A
         16     4 Serializable CacheKey.key                   N/A
         20     4         Type CacheKey.type                  N/A
         24     4       String TenantAwareCacheKey.tenantId   N/A
         28     4              (loss due to the next object alignment)
    Instance size: 32 bytes (estimated, the sample instance is not available)
    Space losses: 0 bytes internal + 4 bytes external = 4 bytes total