[api] Add zero-copy support for noise encryption key requests (#12405)

esphome/core/helpers.cpp

@@ -479,10 +479,14 @@ std::string base64_encode(const uint8_t *buf, size_t buf_len) {
 }
 
 size_t base64_decode(const std::string &encoded_string, uint8_t *buf, size_t buf_len) {
-  int in_len = encoded_string.size();
+  return base64_decode(reinterpret_cast<const uint8_t *>(encoded_string.data()), encoded_string.size(), buf, buf_len);
+}
+
+size_t base64_decode(const uint8_t *encoded_data, size_t encoded_len, uint8_t *buf, size_t buf_len) {
+  size_t in_len = encoded_len;
   int i = 0;
   int j = 0;
-  int in = 0;
+  size_t in = 0;
   size_t out = 0;
   uint8_t char_array_4[4], char_array_3[3];
   bool truncated = false;
@@ -490,8 +494,8 @@ size_t base64_decode(const std::string &encoded_string, uint8_t *buf, size_t buf
   // SAFETY: The loop condition checks is_base64() before processing each character.
   // This ensures base64_find_char() is only called on valid base64 characters,
   // preventing the edge case where invalid chars would return 0 (same as 'A').
-  while (in_len-- && (encoded_string[in] != '=') && is_base64(encoded_string[in])) {
-    char_array_4[i++] = encoded_string[in];
+  while (in_len-- && (encoded_data[in] != '=') && is_base64(encoded_data[in])) {
+    char_array_4[i++] = encoded_data[in];
     in++;
     if (i == 4) {
       for (i = 0; i < 4; i++)