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/Helpers/CustomReader.hpp

@@ -0,0 +1,26 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2022, Benoit BLANCHON
+// MIT License
+
+#pragma once
+
+#include <sstream>
+
+class CustomReader {
+  std::stringstream _stream;
+
+ public:
+  CustomReader(const char* input) : _stream(input) {}
+
+  int read() {
+    return _stream.get();
+  }
+
+  size_t readBytes(char* buffer, size_t length) {
+    _stream.read(buffer, static_cast<std::streamsize>(length));
+    return static_cast<size_t>(_stream.gcount());
+  }
+
+ private:
+  CustomReader(const CustomReader&);
+};