Tuya rgb support (#2278)

Co-authored-by: Oxan van Leeuwen <oxan@oxanvanleeuwen.nl>
Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

esphome/core/helpers.cpp

@@ -270,6 +270,39 @@ optional<int> parse_int(const std::string &str) {
     return {};
   return value;
 }
+
+optional<int> parse_hex(const char chr) {
+  int out = chr;
+  if (out >= '0' && out <= '9')
+    return (out - '0');
+  if (out >= 'A' && out <= 'F')
+    return (10 + (out - 'A'));
+  if (out >= 'a' && out <= 'f')
+    return (10 + (out - 'a'));
+  return {};
+}
+
+optional<int> parse_hex(const std::string &str, size_t start, size_t length) {
+  if (str.length() < start) {
+    return {};
+  }
+  size_t end = start + length;
+  if (str.length() < end) {
+    return {};
+  }
+  int out = 0;
+  for (size_t i = start; i < end; i++) {
+    char chr = str[i];
+    auto digit = parse_hex(chr);
+    if (!digit.has_value()) {
+      ESP_LOGW(TAG, "Can't convert '%s' to number, invalid character %c!", str.substr(start, length).c_str(), chr);
+      return {};
+    }
+    out = (out << 4) | *digit;
+  }
+  return out;
+}
+
 uint32_t fnv1_hash(const std::string &str) {
   uint32_t hash = 2166136261UL;
   for (char c : str) {