Add Home Assistant controls over MQTT

Upgrade ArduinoHA from 1.3.0 to 2.1.0 and rewrite mqtt.ino for it.
The clock now shows up in Home Assistant (discovery prefix
"homeassistant") with:
- switches Tubes (blank the display, runtime only) and Auto dim
- numbers Day/Night brightness
- light Backlight (on/off, brightness, RGB mapped to the colour wheel)
- select LED effect, button Cathode protect
- sensors Light (LDR) and WiFi signal, plus the upstream sensors when
  the clock has them; master-clock subscriptions are kept

Settings changed from HA are saved to EEPROM 3 s after the last change.
Fixes the unbounded memcpy in the MQTT message handler.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

firmware/uniclock/lib/arduino-home-assistant/src/utils/HANumeric.cpp

@@ -0,0 +1,214 @@
+#include "HANumeric.h"
+
+const uint8_t HANumeric::MaxDigitsNb = 19;
+
+HANumeric HANumeric::fromStr(const uint8_t* buffer, const uint16_t length)
+{
+    if (length == 0) {
+        return HANumeric();
+    }
+
+    const uint8_t* firstCh = &buffer[0];
+    int64_t out = 0;
+    bool isSigned = false;
+
+    if (*firstCh == '-') {
+        isSigned = true;
+        firstCh++;
+    }
+
+    uint8_t digitsNb = isSigned ? length - 1 : length;
+    if (digitsNb > MaxDigitsNb) {
+        return HANumeric();
+    }
+
+    uint64_t base = 1;
+    const uint8_t* ptr = &buffer[length - 1];
+
+    while (ptr >= firstCh) {
+        uint8_t digit = *ptr - '0';
+        if (digit > 9) {
+            return HANumeric();
+        }
+
+        out += digit * base;
+        ptr--;
+        base *= 10;
+    }
+
+    return HANumeric(isSigned ? out * -1 : out);
+}
+
+HANumeric::HANumeric():
+    _isSet(false),
+    _value(0),
+    _precision(0)
+{
+
+}
+
+HANumeric::HANumeric(const float value, const uint8_t precision):
+    _isSet(true),
+    _precision(precision)
+{
+    _value = value * static_cast<float>(getPrecisionBase());
+}
+
+HANumeric::HANumeric(const int8_t value, const uint8_t precision):
+    _isSet(true),
+    _precision(precision)
+{
+    _value = value * static_cast<int32_t>(getPrecisionBase());
+}
+
+HANumeric::HANumeric(const int16_t value, const uint8_t precision):
+    _isSet(true),
+    _precision(precision)
+{
+    _value = value * static_cast<int32_t>(getPrecisionBase());
+}
+
+HANumeric::HANumeric(const int32_t value, const uint8_t precision):
+    _isSet(true),
+    _precision(precision)
+{
+    _value = value * static_cast<int32_t>(getPrecisionBase());
+}
+
+HANumeric::HANumeric(const uint8_t value, const uint8_t precision):
+    _isSet(true),
+    _precision(precision)
+{
+    _value = value * getPrecisionBase();
+}
+
+HANumeric::HANumeric(const uint16_t value, const uint8_t precision):
+    _isSet(true),
+    _precision(precision)
+{
+    _value = value * getPrecisionBase();
+}
+
+HANumeric::HANumeric(const uint32_t value, const uint8_t precision):
+    _isSet(true),
+    _precision(precision)
+{
+    _value = value * getPrecisionBase();
+}
+
+#ifdef ARDUINOHA_INT_OVERLOAD
+HANumeric::HANumeric(const int value, const uint8_t precision):
+    _isSet(true),
+    _precision(precision)
+{
+    _value = value * static_cast<int>(getPrecisionBase());
+}
+#endif
+
+HANumeric::HANumeric(const int64_t value):
+    _isSet(true),
+    _value(value),
+    _precision(0)
+{
+
+}
+
+uint32_t HANumeric::getPrecisionBase() const
+{
+    // using pow() increases the flash size by ~2KB
+    switch (_precision) {
+    case 1:
+        return 10;
+
+    case 2:
+        return 100;
+
+    case 3:
+        return 1000;
+
+    default:
+        return 1;
+    }
+}
+
+uint8_t HANumeric::calculateSize() const
+{
+    if (!_isSet) {
+        return 0;
+    }
+
+    int64_t value = _value;
+    const bool isSigned = value < 0;
+
+    if (isSigned) {
+        value *= -1;
+    }
+
+    uint8_t digitsNb = 1;
+    while (value > 9) {
+        value /= 10;
+        digitsNb++;
+    }
+
+    if (isSigned) {
+        digitsNb++; // sign
+    }
+
+    if (_precision > 0) {
+        if (value == 0) {
+            return 1;
+        }
+
+        // one digit + dot + decimal digits (+ sign)
+        const uint8_t minValue = isSigned ? _precision + 3 : _precision + 2;
+        return digitsNb >= minValue ? digitsNb + 1 : minValue;
+    }
+
+    return digitsNb;
+}
+
+uint16_t HANumeric::toStr(char* dst) const
+{
+    char* prefixCh = &dst[0];
+    if (!_isSet || _value == 0) {
+        *prefixCh = '0';
+        return 1;
+    }
+
+    int64_t value = _value;
+    const uint8_t numberLength = calculateSize();
+    if (value < 0) {
+        value *= -1;
+        *prefixCh = '-';
+        prefixCh++;
+    }
+
+    if (_precision > 0) {
+        uint8_t i = _precision;
+        char* dotPtr = prefixCh + 1;
+        do {
+            *prefixCh = '0';
+            prefixCh++;
+        } while(i-- > 0);
+
+        *dotPtr = '.';
+    }
+
+    char* ch = &dst[numberLength - 1];
+    char* lastCh = ch;
+    char* dotPos = _precision > 0 ? &dst[numberLength - 1 - _precision] : nullptr;
+
+    while (value != 0) {
+        if (ch == dotPos) {
+            *dotPos = '.';
+            ch--;
+            continue;
+        }
+
+        *ch = (value % 10) + '0';
+        value /= 10;
+        ch--;
+    }
+
+    return lastCh - &dst[0] + 1;
+}