Add read-only mmap support (mmap_mode="r") for DictStore, TreeStore, and EmbedStore#585

Karol-G wants to merge 4 commits intoBlosc:mainBlosc/python-blosc2:mainfrom

Karol-G:feat/store_container_mmap_supportKarol-G/python-blosc2:feat/store_container_mmap_supportCopy head branch name to clipboard