net: make the list of known message types a compile time constant

Turn the `std::vector` to `std::array` because it is cheaper and
allows us to have the number of the messages as a compile time
constant: `ALL_NET_MESSAGE_TYPES.size()` which can be used in
future code to build other `std::array`s with that size.

src/test/fuzz/process_message.cpp

@@ -37,7 +37,7 @@ void initialize_process_message()
 {
     if (const auto val{std::getenv("LIMIT_TO_MESSAGE_TYPE")}) {
         LIMIT_TO_MESSAGE_TYPE = val;
-        Assert(std::count(getAllNetMessageTypes().begin(), getAllNetMessageTypes().end(), LIMIT_TO_MESSAGE_TYPE)); // Unknown message type passed
+        Assert(std::count(ALL_NET_MESSAGE_TYPES.begin(), ALL_NET_MESSAGE_TYPES.end(), LIMIT_TO_MESSAGE_TYPE)); // Unknown message type passed
     }
 
     static const auto testing_setup = MakeNoLogFileContext<const TestingSetup>(