[core] Avoid heap allocation in str_equals_case_insensitive with string literals (#13312)

esphome/core/helpers.h

@@ -572,6 +572,10 @@ template<typename T> constexpr T convert_little_endian(T val) {
 bool str_equals_case_insensitive(const std::string &a, const std::string &b);
 /// Compare StringRefs for equality in case-insensitive manner.
 bool str_equals_case_insensitive(StringRef a, StringRef b);
+/// Compare C strings for equality in case-insensitive manner (no heap allocation).
+inline bool str_equals_case_insensitive(const char *a, const char *b) { return strcasecmp(a, b) == 0; }
+inline bool str_equals_case_insensitive(const std::string &a, const char *b) { return strcasecmp(a.c_str(), b) == 0; }
+inline bool str_equals_case_insensitive(const char *a, const std::string &b) { return strcasecmp(a, b.c_str()) == 0; }
 
 /// Check whether a string starts with a value.
 bool str_startswith(const std::string &str, const std::string &start);