x.crypto.slhdsa: add a SLH-DSA implementation, a stateless hash-based DSA, a post quantum cryptographic module (#24086)

vlib/x/crypto/slhdsa/examples/example0.v

@@ -0,0 +1,26 @@
+module main
+
+import x.crypto.slhdsa
+
+fn main() {
+	// creates default key
+	mut pvkey := slhdsa.PrivateKey.new()!
+
+	// example of message
+	xmsg := 'Sample message'.bytes()
+
+	// signing the message with the key
+	sig := pvkey.sign(xmsg)!
+
+	// example of public key
+	mut pbkey := pvkey.public_key()!
+
+	// verify signature with the public key
+	verified := pbkey.verify(sig, xmsg)!
+	dump(verified) // true
+	assert verified == true
+
+	// release the resources
+	pvkey.free()
+	pbkey.free()
+}