Thread-safe array views are broken on develop

[lindstro]

With the recent refactoring of the compressed-array classes into array, cache, store, and codec, there is now a single codec, owned by the data store, that is unsafely shared among threads even when thread-private views are used. Prior to the refactoring, each private_const_view and private_view owned a private zfp_stream and bitstream for accessing compressed blocks. This unsafe sharing of state for reading and writing data results in race conditions that corrupt reads and writes. As a result, the diffusion example fails when multithreading is enabled.