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/TextFormatter/writeString.cpp

@@ -0,0 +1,57 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2022, Benoit BLANCHON
+// MIT License
+
+#include <catch.hpp>
+
+#include <ArduinoJson/Json/TextFormatter.hpp>
+#include <ArduinoJson/Serialization/Writers/StaticStringWriter.hpp>
+
+using namespace ARDUINOJSON_NAMESPACE;
+
+void check(const char* input, std::string expected) {
+  char output[64] = {0};
+  StaticStringWriter sb(output, sizeof(output));
+  TextFormatter<StaticStringWriter> writer(sb);
+  writer.writeString(input);
+  REQUIRE(expected == output);
+  REQUIRE(writer.bytesWritten() == expected.size());
+}
+
+TEST_CASE("TextFormatter::writeString()") {
+  SECTION("EmptyString") {
+    check("", "\"\"");
+  }
+
+  SECTION("QuotationMark") {
+    check("\"", "\"\\\"\"");
+  }
+
+  SECTION("ReverseSolidus") {
+    check("\\", "\"\\\\\"");
+  }
+
+  SECTION("Solidus") {
+    check("/", "\"/\"");  // but the JSON format allows \/
+  }
+
+  SECTION("Backspace") {
+    check("\b", "\"\\b\"");
+  }
+
+  SECTION("Formfeed") {
+    check("\f", "\"\\f\"");
+  }
+
+  SECTION("Newline") {
+    check("\n", "\"\\n\"");
+  }
+
+  SECTION("CarriageReturn") {
+    check("\r", "\"\\r\"");
+  }
+
+  SECTION("HorizontalTab") {
+    check("\t", "\"\\t\"");
+  }
+}