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/String.h

@@ -0,0 +1,69 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2022, Benoit BLANCHON
+// MIT License
+
+#pragma once
+
+#include <string>
+
+// Reproduces Arduino's String class
+class String {
+ public:
+  String() : _maxCapacity(1024) {}
+  explicit String(const char* s) : _str(s), _maxCapacity(1024) {}
+
+  void limitCapacityTo(size_t maxCapacity) {
+    _maxCapacity = maxCapacity;
+  }
+
+  unsigned char concat(const char* s) {
+    return concat(s, strlen(s));
+  }
+
+  size_t length() const {
+    return _str.size();
+  }
+
+  const char* c_str() const {
+    return _str.c_str();
+  }
+
+  bool operator==(const char* s) const {
+    return _str == s;
+  }
+
+  String& operator=(const char* s) {
+    _str.assign(s);
+    return *this;
+  }
+
+  char operator[](unsigned int index) const {
+    if (index >= _str.size())
+      return 0;
+    return _str[index];
+  }
+
+  friend std::ostream& operator<<(std::ostream& lhs, const ::String& rhs) {
+    lhs << rhs._str;
+    return lhs;
+  }
+
+ protected:
+  // This function is protected in most Arduino cores
+  unsigned char concat(const char* s, size_t n) {
+    if (_str.size() + n > _maxCapacity)
+      return 0;
+    _str.append(s, n);
+    return 1;
+  }
+
+ private:
+  std::string _str;
+  size_t _maxCapacity;
+};
+
+class StringSumHelper;
+
+inline bool operator==(const std::string& lhs, const ::String& rhs) {
+  return lhs == rhs.c_str();
+}