Load as an undigested dictionary to compressor.
Pass this attribute as zstd_dict argument:
compress(dat, zstd_dict=zd.as_undigested_dict)
1. The advanced compression parameters of compressor will not be
overridden.
2. Loading an undigested dictionary is costly. If load an undigested
dictionary multiple times, consider reusing a compressor object.
3. No need to use this for decompression.