Bugfixes

• fix serialization context passed
• fix a bug which caused module duplication when using persistent caching, unsafe cache and memory cache with GC
• fix validation of snapshots of non-existing directories

Performance

• store a hash in first bits of bigint to workaround v8 hashing: https://github.com/v8/v8/blob/b704bc0958e2e26305a68e89d215af1aee011148/src/objects/bigint.h#L192-L195