feat: add initial experimental Twitch Eventsub support (#5837)

Co-authored-by: nerix <nerixdev@outlook.de>

lib/twitch-eventsub-ws/src/chrono.cpp

@@ -0,0 +1,27 @@
+#include "twitch-eventsub-ws/chrono.hpp"
+
+#include "twitch-eventsub-ws/date.h"
+
+#include <sstream>
+
+namespace chatterino::eventsub::lib {
+
+boost::json::result_for<std::chrono::system_clock::time_point,
+                        boost::json::value>::type
+    tag_invoke(
+        boost::json::try_value_to_tag<std::chrono::system_clock::time_point>,
+        const boost::json::value &jvRoot, const AsISO8601 &)
+{
+    const auto raw = boost::json::try_value_to<std::string>(jvRoot);
+    if (raw.has_error())
+    {
+        return raw.error();
+    }
+
+    std::chrono::system_clock::time_point tp;
+    std::istringstream in{*raw};
+    in >> date::parse("%FT%TZ", tp);
+
+    return tp;
+}
+}  // namespace chatterino::eventsub::lib