Add uint256_to_decimal to replace tostring256

TODO: replace tostring256 everywhere

src/utils.h

@@ -32,6 +32,8 @@ int local_strchr(char* string, char ch);
 // throw if the size is > 4.
 uint32_t u32_from_BE(uint8_t* in, uint8_t size, bool strict);
 
+bool uint256_to_decimal(const uint8_t *value, char *out, size_t out_len);
+
 void amountToString(uint8_t* amount,
                     uint8_t amount_len,
                     uint8_t decimals,