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/MsgPackDeserializer/doubleToFloat.cpp

@@ -0,0 +1,25 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2022, Benoit BLANCHON
+// MIT License
+
+#include <ArduinoJson.h>
+#include <catch.hpp>
+
+using namespace ARDUINOJSON_NAMESPACE;
+
+template <typename T>
+static void check(const char* input, T expected) {
+  T actual;
+  uint8_t* f = reinterpret_cast<uint8_t*>(&actual);
+  const uint8_t* d = reinterpret_cast<const uint8_t*>(input);
+  doubleToFloat(d, f);
+  fixEndianess(actual);
+  CHECK(actual == expected);
+}
+
+TEST_CASE("doubleToFloat()") {
+  check("\x40\x09\x21\xCA\xC0\x83\x12\x6F", 3.1415f);
+  check("\x00\x00\x00\x00\x00\x00\x00\x00", 0.0f);
+  check("\x80\x00\x00\x00\x00\x00\x00\x00", -0.0f);
+  check("\xC0\x5E\xDC\xCC\xCC\xCC\xCC\xCD", -123.45f);
+}