Import ESP_UniClock (upstream 1189810)

Vendored from https://github.com/gpeter62/ESP_UniClock: the sketch
source, the web UI and the libraries the ESP8266 build needs, unpacked
from the bundled zips. Adds a PlatformIO project for the ESP-12. The
source is unchanged; local changes follow as separate commits.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

firmware/uniclock/lib/ArduinoJson/extras/tests/JsonSerializer/misc.cpp

@@ -0,0 +1,36 @@
+#include <ArduinoJson.h>
+#include <catch.hpp>
+#include <limits>
+
+TEST_CASE("serializeJson(MemberProxy)") {
+  DynamicJsonDocument doc(4096);
+  deserializeJson(doc, "{\"hello\":42}");
+  JsonObject obj = doc.as<JsonObject>();
+  std::string result;
+
+  serializeJson(obj["hello"], result);
+
+  REQUIRE(result == "42");
+}
+
+TEST_CASE("serializeJson(ElementProxy)") {
+  DynamicJsonDocument doc(4096);
+  deserializeJson(doc, "[42]");
+  JsonArray arr = doc.as<JsonArray>();
+  std::string result;
+
+  serializeJson(arr[0], result);
+
+  REQUIRE(result == "42");
+}
+
+TEST_CASE("serializeJson(JsonVariantSubscript)") {
+  DynamicJsonDocument doc(4096);
+  deserializeJson(doc, "[42]");
+  JsonVariant var = doc.as<JsonVariant>();
+  std::string result;
+
+  serializeJson(var[0], result);
+
+  REQUIRE(result == "42");
+}