Fix: fix eval hang

[GregoryLi360]

fix eval <file> computed correctly but hung on shutdown (closes #40, regression after #39). Drop ran before kernel::shutdown(), which called the Close path for the first time which had 2 bugs:

• Host never acked Close, but caller expects it and blocks waiting for it
• After the host sends the ack response, arca panics with Err(Closed) because Reader::read reported the pipe being closed before reading the ack

Also updated README just fix eval addblob.fix