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/MemoryPool/clear.cpp

@@ -0,0 +1,32 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2022, Benoit BLANCHON
+// MIT License
+
+#include <ArduinoJson/Memory/MemoryPool.hpp>
+#include <ArduinoJson/Strings/StringAdapters.hpp>
+#include <catch.hpp>
+
+using namespace ARDUINOJSON_NAMESPACE;
+
+static const size_t poolCapacity = 512;
+
+TEST_CASE("MemoryPool::clear()") {
+  char buffer[poolCapacity];
+  MemoryPool pool(buffer, sizeof(buffer));
+
+  SECTION("Discards allocated variants") {
+    pool.allocVariant();
+
+    pool.clear();
+    REQUIRE(pool.size() == 0);
+  }
+
+  SECTION("Discards allocated strings") {
+    pool.saveString(adaptString(const_cast<char *>("123456789")));
+    REQUIRE(pool.size() == 10);
+
+    pool.clear();
+
+    REQUIRE(pool.size() == 0);
+  }
+}