Otherwise there was going to be unexpected behaviour if
`BytesMessage.freeze()` was called followed by
`BytesMessage.release()`.

Accidentally left testing branch name in actions, switched to
triggering on release tags.

The produced name of package files is correct and should be left alone.

In the same ways as Message.ident, using a bytes string with a length
of one would eventually cause issues.  It also maintains the ability to
set/compare the value to a Message.ident value.

Store the ident value as an integer instead of a byte string with
a length of one, which would inevitably cause trouble somewhere.

Also incidentally fixes an issue packing/unpacking messages in the
unlikely event that a message is greater than 2^31 bytes due to using
a signed integer type for the message size.

This option allows users to pretend that Abort was sent when an unknown
message is received.

Closes #2

No-response messages need to be configured through Negotiate messages
passed between the MTA and filter.

This is specifically for Flakeheaven's cache, which does not (yet)
include automatic .gitignore