[NEW] security/sequoia-sq (and dependency devel/capnproto)

I'd like to propose to import sequoia-sq (https://sequoia-pgp.org)

"sq is a command-line tool for working with OpenPGP artifacts with a
focus on usability, security, and robustness"

It requires Cap'n Proto (https://capnproto.org/) as a build dependency.

"Cap'n Proto is a fast data interchange format and capability-based RPC
system."

Tested on amd64 so far. Thoughts? Opinions? oks?