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/api/Stream.h

@@ -0,0 +1,14 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2022, Benoit BLANCHON
+// MIT License
+
+#pragma once
+
+// Reproduces Arduino's Stream class
+class Stream  // : public Print
+{
+ public:
+  virtual ~Stream() {}
+  virtual int read() = 0;
+  virtual size_t readBytes(char *buffer, size_t length) = 0;
+};