RTG-1339 Support post-quantum hybrid key exchange

Func spec: https://wiki.cfops.it/x/ZcBKHw

vendor/github.com/cloudflare/circl/dh/x25519/curve_noasm.go

@@ -0,0 +1,11 @@
+//go:build !amd64 || purego
+// +build !amd64 purego
+
+package x25519
+
+import fp "github.com/cloudflare/circl/math/fp25519"
+
+func double(x, z *fp.Elt)             { doubleGeneric(x, z) }
+func diffAdd(w *[5]fp.Elt, b uint)    { diffAddGeneric(w, b) }
+func ladderStep(w *[5]fp.Elt, b uint) { ladderStepGeneric(w, b) }
+func mulA24(z, x *fp.Elt)             { mulA24Generic(z, x) }