Quantum-resistant crypto

per https://github.com/vector-im/element-web/issues/8889

see also https://github.com/matrix-org/matrix-spec/issues/934
see also https://github.com/matrix-org/matrix-spec/issues/932

----

Wire has done this: https://wire.com/en/blog/post-quantum-resistance-wire/

Disclaimer: I have no idea what this entails.