I want gocryptfs to support a -zerokey CLI option for automated tests and other explicitly insecure test…

I want gocryptfs to support a -zerokey CLI option for automated tests and other explicitly insecure test…: a task in MiMo-V2.6-RL-harbor-code: MiMo-V2.6-RL Code (Harbor) (Harbor dataset). For observability, using -zerokey should print informational output that says an all-zero dummy master key is…

The task

For observability, using `-zerokey` should print informational output that says an all-zero dummy master key is being used and warns that this mode provides no security and is only for testing. `gocryptfs -hh` should list `-zerokey` with a short description such as "Use all-zero dummy master key". The option should…

Part of FineEnvs/MiMo-V2.6-RL-harbor-code.